Ryuga Banjo

Ryuga Banjo (万丈 龍我) is a 23-year-old ex-fighter who was wrongly imprisoned for the murder of Takumi Katsuragi, a scientist studying the Pandora Box. Abducted by Faust while in prison, Ryuga managed to escape with his humanity intact, which would lead him to join Sento Kiryu in uncovering the truth behind their shared experiences as Faust victims.

After borrowing Sento's Build Driver and later receiving a newly made one from Sento himself, he uses the Cross-Z Dragon given to him by Sento in conjunction with the Dragon Fullbottle left by his late girlfriend Kasumi Ogura to become Kamen Rider Cross-Z (仮面ライダークローズ), the secondary rider of Kamen Rider Build.

As war broke out between Hokuto and Touto, Ryuga took the Sclash Driver against Sento's objections and used it in conjunction with the Dragon Sclashjelly to become Kamen Rider Cross-Z Charge (仮面ライダークローズチャージ) until the Sclash Driver and Sclashjelly were destroyed by Blood Stalk. The remains of the Dragon Sclashjelly were used to create the Dragon Magma Fullbottle, allowing Ryuga to use in conjunction with the Cross-Z Magma Knuckle to transform into Kamen Rider Cross-Z Magma (仮面ライダークローズマグマ).

In Episode 31, it is revealed that Ryuga is not a human and possesses some of Evolto's DNA, the being which destroyed life on Mars. Evolto eventually possessed Ryuga and became one once again. However, they were soon separated and Evolto's DNA was removed from Ryuga as a result, thus stripping Ryuga of his transformation abilities. However Ryuga steals Evolto's Dragon Evolbottle and it transforms into the Great Dragon Evolbottle, reenabling Ryuga to transform once again and accesses a new form, Kamen Rider Great Cross-Z (仮面ライダーグレートクローズ).

Arrival on Earth
In 1994, 13 years before Sky Wall Incident, an unmanned space probe from Japan landed successfully on Mars and returned to Earth. After its return to the Nanba Heavy Industries Institute of Synthetic Science, the probe unexpectedly brought back an alien specimen in the form of glowing red slug-like creature, later revealed to be a portion of Evolto, deliberately sent to the probe, with the intent of finding another planet to destroy. His specimen made its way out of the probe and attempted to possess and plant itself into Yuri Banjo, a security guard who was stationed there with her husband. Instead, the specimen ended up possessing Ryuga as a fetus, causing her to fall unconscious while on duty. During a checkup at a hospital, she was discovered to be one month pregnant, which was the suspected reasoning behind her collapse.

A month later, Ryuga was born in Yokohama, but all the memories and powers the specimen possessed was lost, leaving Ryuga as human. To everyone's bewilderment, the child was in perfect health, weighing 3.2 kg despite his two-month gestation period. Because of this oddity, he was examined at a university hospital, discovering a cellular structure never before seen in humans in him. He was later be re-examined at the Namba Heavy Industries Institute of Synthetic Science, discovering his genes are of extraterrestrial origin. This resulted in periodic examinations from the Institute, under the supervision of Shinobu Katsuragi, until his parents' death.

Ryuga lost his parents in an accident at the age of 13. Ryuga doesn't remember the details of the accident or even his past experiments, which he attributes to the trauma of the event. He was placed in the care of relatives. Around this time, Ryuga was introduced to Soichi Isurugi, who also shared Evolto's essence (although Evolto's consciousness had completely overwhelmed Isurugi).

Present
As an adult, Ryuga became a professional fighter, eventually getting engaged to Kasumi Ogura. By the age of 22, Ryuga earned a lifelong ban from fighting for throwing a match; it is implied that he accepted a bribe in order to pay for the frail Kasumi's medical bills. To help his search for a new job, Kasumi directed Ryuga to Takumi Katsuragi, a researcher at the Touto Institute of Advanced Matter Physics, who was apparently looking for an assistant (which turned out to be a ploy by Katsuragi to lure him and Evolto into his trap to destroy them both). However, when Ryuga came to Katsuragi's home to apply, he found the corpse of "Katsuragi" inside. Moments later, Touto's Guardians arrived and apprehended Ryuga. It would be revealed that it was Soichi Isurugi who called Ryuga the murderer, which would give Ryuga a ten-year sentence in prison.

While in prison, he was attacked by a prison guard working for Faust, who injected him with Nebula Gas. However, Ryuga's naturally high Hazard Level allowed him to escape mid-experiment with his memories and humanity intact. After fighting off the Faust scientists, he retreated to the sewers.

The Rabbit Tank Meets Dragon
Ryuga was eventually found by Touto's Guardians, who attempted to recapture him. Ryuga managed to fend off the Guardians and escaped before he was apprehended by Sento Kiryu, who had tracked him upon noticing his Smash-like energy readings. Upon realizing that Ryuga had undergone a similar experience, Sento began interrogating Ryuga in hopes of uncovering his past, despite Ryuga's frustrated belligerence. The two were interrupted by Strong Smash, who attacked Ryuga. However, Ryuga was saved by Sento, who transformed into Kamen Rider Build and defeated the Smash. Ryuga recognized the Smash's human identity as one of his fellow victims but was frustrated to find that the man had no memories of the experiments. The Touto government arrived soon after to retake Ryuga. Sento, believing in Ryuga's innocence, helped him escape.

Burn Smash incident
Sento brought Ryuga to the basement lab of the nascita café, where the former had been living for the last year. After meeting Sento's accomplices, Souichi and Misora Isurugi, Ryuga explained the circumstances that resulted in his arrest. However, the story was interrupted by Sawa Takigawa, a freelance journalist who had entered the base (due to Souichi and Sento's carelessness).

As a precaution, Ryuga was chained up in the lab, much to his chagrin. Misora took the time to explain the Fullbottle purification process to Ryuga, as well as Sento's job. Noticing Misora's smartphone, Ryuga goaded her into proving her ability to purify Smash energy. As planned, Misora left her smartphone where Ryuga could reach it, allowing him to contact Kasumi. However, much to his horror, Kasumi had been kidnapped by Faust as well. Given Kasumi's location by Night Rogue, Ryuga broke out of Nascita and raced to save his fiancé. After another encounter with Guardians (which ended with being saved again by Build), Ryuga explained his motives to Sento but choked him into unconsciousness to prevent him from getting involved.

When Ryuga finally arrived at the location, he learned that he was too late: Kasumi had already been transformed into the Burn Smash. Unable to see his beloved hurt, Ryuga begged Sento not to attack her when the latter arrived. The two were quickly overwhelmed by the Smash and Night Rogue, upon which the latter revealed the horrifying truth: Kasumi's body was too weak, and removing her Smash element would be fatal. Realizing that Kasumi could not be saved, Ryuga begged to Build to end her suffering. Sento was able to separate Kasumi's consciousness long enough for her and Ryuga to say their goodbyes. Left almost broken by grief, Ryuga would have let himself be captured again if not for Sento, who reminded him that it would all be for nothing if he got arrested again. Kasumi's Smash essence was purified into the Dragon Fullbottle, which Sento gave to Ryuga as a memento of his beloved. Soon after, Sawa arrived, having discovered the identity of the guard who attacked Ryuga: Masahiro Nabeshima.

Continuing the Search
After some searching, Ryuga managed to contact Nabeshima. Nabeshima revealed that his family was being threatened by Faust, upon which Ryuga offered to smuggle them out of Seito to safety in exchange for Nabeshima testifying for his innocence (not realizing this was a trap set up by Night Rogue). With Sawa's help, Ryuga snuck to Seito. Upon retrieving Nabeshima's wife and daughter, Ryuga and Sawa were attacked by hijacked Guardians, barely escaping with their lives. Ryuga arrived in Touto to aid Build in taking down Nabeshima, who had been subjected to two Smash transformations by Faust. While Nabeshima was returned to his human form, the experiments wiped his memory clean, leaving him unable to recognize his daughter, let alone testify for Ryuga.

The next lead came in the form of Tatsuya Kishida, who was roommates (as well as bandmates) with Sento before the latter lost his memory.

Becoming Cross-Z
With the Dragon Fullbottle synchronized to Ryuga for so long, Sento decides to use Cross-Z Dragon to make Ryuga a rider. But his obsession to kill "Katsuragi" got rejected by the adapter to transform. Reading a letter written by Kasumi, he was renewed to finally use Cross-Z to finally become a Kamen Rider named Cross-Z.

On November 30th, Ryuga and Sento were neutralizing a Strong Smash Hazard when they rescued a mysterious young man named Sougo Tokiwa, who claimed to hail from one year into the future. Taking him with them to back nascita, Sento examined the Ridewatch on Sougo's person, confirming through its technology that it did indeed hail from a future time period as Sougo had claimed. Soon after, Tsukuyomi entered nascita, using her Faiz Phone X to stun all three men before returning Sougo to his own time.

Learning Sento Kiryu's True Identity
When Ryuga found out that Sento was actually Katsuragi himself, he became really angry as he thought it was Sento's fault his fiancee was dead. This event led him having Sento fight him, in order to let out his hate towards him. In the end, Build RabbitTank Sparkling beat Cross-Z.

Cross-Z charges up
In one fight, Ryuga was granted the Kuma and Televi Fullbottles by Grease as a concession when the Hokuto Three Crows interfered in their battle and breaking the rules. After giving the new pair to Sento, Ryuga saw that nascita finally had a customer in the form of Massugu Ubukata. Providing his customer with a canned coffee, Ryuga, foreseeing a boon in business, set out to acquire a bountiful stock of coffee beans, only to find the shop as vacant as usual when he returned.

Cross-Z Charges into Hell
Seito proposes a 3-on-3 representative battle to Touto. Ryuga is participating Round 2 against Fu Washio. Much to the surprise of Ryuga, the announcement depicts the name his opponent is "Hell Bro's", which he had never heard before. As Ryuga prepare his transformation, he is interrupted by the sudden appearance of the Gear Engine on Fu's hands. Fu uses it along with his personal Gear Remocon to transform into Hell Bro's, completely overwhelming Ryuga's expectations. However, Ryuga didn't waver and proceed to transform into Cross-Z Charge.

As Cross-Z Charge and Hell Bro's goes down on a fierce fight, Ryuga determination to not let Sento burden himself and end the war manage to overwhelm Hell Bro's. But, Fu suddenly claims that if he about to lose this proxy battle, Rai will be executed. Ryuga was torn between saving Touto or saving Rai as Fu take his chance to soundly defeat Ryuga. Fu later mocks Ryuga by being too gullible as he fell to Fu trick, showing that Rai is in fact, never get captured Hostage. Although visibly frustrated, Ryuga accepts his loss and exclaiming that Sento will be the one who ends the war before leaving.

Ryuga's predictions came out true as Build manage to defeat Rogue using TankTank form, and Ryuga celebrates Sento victory along with Misora, much to Kazumi ire.

Sclash Driver Destroyed, and Going Magma
"Good, Banjo! Show me how powerful you are!" "Just what I wanted!"

- Cross-Z Magma unveiling his new power to Blood Stalk. After Vernage resurfaced from Misora's bracelet, Blood Stalk got his transformation knocked out after the queen blew a strong gust of wind at him. He then tried to attack her again, but Ryuga stood in the way. However, this resulted in Ryuga's Sclash Driver getting destroyed, and the Dragon Sclashjelly overheated to a burnt ball of ash.

Back in nascita, the Dragon Sclashjelly reacted to Ryuga's emotions, creating the Dragon Magma Fullbottle. Seeing this, Sento later made the Cross-Z Magma Knuckle for Ryuga to use with it as it was too dangerous for the Build Driver alone. This, in turn, helped Ryuga fight off Blood Stalk and Hell Bro's with ease.

In the middle of dealing with Hell Bro's, Gentoku entered the scene, transformed into Rogue, fought, and sneakily explained what was actually Stalk's plan by whispering to them on every single strike he did. The truth was shocking for Ryuga as Rogue declared that he was not human and was the target for Stark not just by chance, especially on why Kasumi was kidnapped and killed. All of this was to give Ryuga his power and increase it over time.

After Sento knocked down Gentoku, he, Ryuga, and Kazumi went and found Stalk. As Stalk went serious, his strength proved to be far stronger than Build RabbitRabbit Form and had Kazumi knocked down unconscious. Ryuga asked Stalk if what Gentoku had told was the truth, shocking Stalk and claiming that it was true, making Ryuga mad but still unable to beat him.

As Stalk was about to kill Sento, Ryuga's anger became stronger which finally stabilized the Dragon Magma Fullbottle. Despite not being told about Cross-Z Magma Knuckle's ability to evolve his form, Ryuga used the Cross- Z Magma Knuckle and the Dragon Magma Fullbottle to transform into Cross-Z Magma. His new form was able to knock down Stalk and give him the chance to take Pandora Box as well as save the others.

Ryuga, the Human Race's End? & Possessed by Evolto
Ryuga was told by Evolto that he was the same as him, the one who would destroy the world. Albeit initially refusing to acknowledge it, Ryuga finally determined to use his power as a Kamen Rider to fight for love and peace, the very same ideal that Sento believes in and strongly holds onto. When Evolto finally regains his Evol Driver and becomes Kamen Rider Evol, poisoning Sento, he makes Ryuga give Pandora's Box and Touto's bottles to him in order to cure his fallen friend. While waiting, Evolto reveals the truth behind his framing and imprisonment & how Ryuga's genes are connected to him. He also reveals that Katsuragi planned on luring him and Ryuga to destroy them both in an apartment, after researching their origins. Ryuga was in disbelief on what Katsuragi intended to do before becoming Sento.

Later on, Ryuga was possessed by Evolto, as his Hazard Level had reached 5, the amount needed to use the Evol-Driver, becoming Evol Dragon Form.

Powers Restored, Katsuragi's Return & The Lost Bottles
Receiving a mysterious invitation, Ryuga was met by what appeared to be the new Prime Minister of Seito, Mitsuomi Gohara. "Mitsuomi" was, however, one of the Blood Tribe, a member of the same race as Evolto who had been operating behind the scenes. "Mitsuomi" claimed responsibility for the experiment which transformed Kasumi Ogura into a Smash, a revelation which enraged Ryuga who proceeded to attack the Prime Minister, who transformed into the Zebra Lost Smash. However, the fight was soon interrupted by "Kengo Ino", who overpowered and took control of Ryuga, compelling him to confront and attack Sento. Confiscating the Hazard Trigger, Ryuga provided the device to "Kengo Ino" who used it with Ryuga's own Great Cross-Z Dragon along with a Build Driver and the Cobra Lost Fullbottle to transform into Kamen Rider Blood, combining his power with Ryuga and his fellow Blood Tribe members.

Rescued from Blood's mercy by Evolto, Sento was intent on saving Ryuga. Realizing that a duo of Fullbottles in the Build Driver could allow him and Ryuga to defeat evil together, Sento soon confronted the Blood Tribe and the possessed Ryuga. Though outmatched by Blood, Build was able to land a blow which seperated Ryuga from him, proceeded to clear Ryuga's mind with the power of the Genius Fullbottle. Though faced by the Lost Smash and the compelled civilian masses, Sento and Ryuga were covered by Grease and Rogue. Presenting the Gold Rabbit and Silver Dragon Fullbottles, Sento revealed to Ryuga that they could both use this pair of Fullbottles to fight together. Though Ryuga was skeptical, Misora channeled the power of Vernage to combine the Fullbottles with the Genius Fullbottle, resulting in the creation of the Cross-ZBuild Can, a device which enabled a transformation combining Sento and Build into Kamen Rider Cross-ZBuild, much to Ryuga's shock. Ultimately, this new power proved great enough to destroy Kamen Rider Blood, though it reverted back to the Genius Fullbottle shortly after.

Personality
1="Give me strength."

- Ryuga's request to Kasumi, via the Dragon Fullbottle, before transforming for the first time into Kamen Rider Cross-Z.

2="Why...? No one asked them to... No one's ever gonna appreciate it! Why do they keep fighting after being beaten up like that?! They're all stupid! But... That's not so bad. I fight for my own sake... For the people I believe in... And the people that believe in me!"

- Witnessing the Legend Riders' fights, Ryuga understands the reason for becoming a Kamen Rider.

3="Even if I'm not human...Even if I have the same power as you...We are different. If you will destroy the world with this power...then I...will use it to bring about love and peace. That's the Kamen Rider I believe I am!"

- Ryuga's resolve to stand against Evolto despite his true origins.

4="Not yet... I'll stand up... As many times as I have to..."

- Ryuga's resolve to save Sento, who had been possessed by Evolto.

Ryuga is a hot-blooded and impulsive man, tending to lash out quickly. While nowhere near as intelligent as Sento, Ryuga prefers to confront problems directly using his fists and doesn't want to involve other people in his own problems. Also, unlike Sento, he does not overthink things, preferring to use common sense, as shown when he was easily able to guess two Best Matches on his own. He is shown to easily get startled, especially when the bell goes off indicating a Fullbottle is ready.

Despite being a capable fighter, Ryuga is shown to be easily provoked in most situations. When combined with the priority to prove his innocence, it sometimes caused a major sidetrack in Build's battles against Smash (such as transforming Tatsuya back into Press Smash just to locate Faust's base) without even forming the next phase of his plans.

Beneath his tough exterior is an honest, selfless and honorable individual. It is implied that the cheating that banned him from fighting was to get money for his fiancée's medical treatments. Ryuga also has a friendly side, such as when he encourages Takehiko after Build removed the Smash essence from him.

Ryuga is also shown to have a protective side, as when he attacked Blood Stalk out of anger for the sake of both Sento and Misora, completely disregarding the fact that Stalk framed him. He also directly apologized to Sento on his behalf to the remaining Hokuto Three Crows, partially blaming himself due to letting Sento use Hazard Trigger for his own sake.

Upon constant usage of the Sclash Driver, Ryuga's personality becomes more aggressive with the single task of getting stronger and beating down his opponent. These side effects also remove his rationality to make decisions, but he is able to overcome these weaknesses with his strong will to save Sento from rampaging with the Hazard Trigger.

Because Banjo has Evolto's DNA in him, he becomes more violent and tends to go berserk whenever Evolto's memories are unveiled. These side effects have been nullified however, after Vernage's DNA was implemented into Banjo's body, while trying to save Misora.

Ryuga appears to hold a lot of fondness for his childhood, as whenever he describes the circumstances of his birth, a bright smile is always on his face.

Powers and Abilities

 * Hand-to-Hand Combat: Ryuga is a skilled fighter, having fought professionally before being banned for life after a bribing incident.
 * Smash Energy Signature: After he had escaped after being exposed to the Nebula Gas, Ryuga gave off an energy signature similar to a Smash, which had alerted Sento to his location.
 * Extraterrestrial Physiology: Ryuga's body was created from Evolto's essence, brought back from a Martian probe. This allows him to utilize the Pandora Box's power like Stalk (albeit unintentionally) and absorb the same power needed to complete the Dragon Magma Fullbottle. Furthermore, his eyes will glow red while doing so.
 * High Hazard Level: Initially, Ryuga's Hazard Level had been above 2.0, allowing him to retain his humanity after his exposure to the Nebula Gas while still gaining physiological powers from it. According to Blood Stalk, while fighting, Ryuga can raise his Hazard Level, having raised it as far as 2.7 in their fight. Eventually, he was able to raise his Hazard Level to 3.0, which is high enough to use the Build Driver. Continued fighting as Cross-Z allowed him to quickly raise it even further to 4.0, enabling him to use the Sclash Driver.  During his fight with Evolto before being possessed by him, his Hazard Level had been measured to be at 4.7, 4.9, and finally 5, a Hazard Level that an ordinary human cannot supposedly achieve unless via special means.  After remembering the destruction of Mars when he was part of Evolto, Ryuga's Hazard Level rose to 7.
 * Hazard Level Escalation: Although the full extent is unclear, Ryuga's Hazard Level grows at a faster rate than any other Kamen Rider, to the point where his strength grows noticeably in a single fight, forcing his opponents to resort to low blows.
 * Superhuman Strength: Ryuga has displayed enhanced strength: he was able to fight off numerous Guardians on his own, and break metal chains with his bare hands.
 * Pandora Box Manipulation: His true alien origin allows him to manipulate the structure of the Sky Wall by touching the Pandora Box.
 * Fullbottle Augmentation: By holding a Fullbottle, or Evolbottle in his hand while untransformed, Ryuga can gain abilities based on said Fullbottle's traits:
 * Dragon Fullbottle: Ryuga's punches give off powerful shockwaves. Notably, his strong synchronization with the Dragon Fullbottle causes his power to increase with each use. Currently, Ryuga's synchronization is high enough that he can defeat a Hazard Smash while untransformed.
 * Dragon/Great Dragon Evolbottle: Similar to the effects of the normal Dragon Fullbottle, Ryuga can perform powerful punches. However, Ryuga's punches are now strong enough that they are able to damage Kamen Rider Evol.

Weaknesses

 * Sclash Driver (Formerly): Although the Sclash Driver can grant Ryuga tremendous power, prolonged usage can slowly turn him into a more aggressive person and give him an addiction to battle. Furthermore, the driver administers electrical shockwaves to the user after a period of time, canceling his transformation and rendering him unconscious. After learning from Sawa that Sento built a failsafe to destroy the Hazard Trigger and kill himself, Banjo overcomes his guilt and turns into Cross-Z Charge to stop Sento in his HawkGatling Hazard form. During the fight, the Sclash Driver began to increase his aggressiveness, yet he managed to overcome it by reminding himself to save Sento, thus gaining control over his Cross-Z Charge form.
 * Cross-Z Magma Form: While utilizing Cross-Z Magma, the suit will increase in heat over the course of the battle, eventually resulting in the suit becoming flammable and extert intense pain to Ryuga due to the massive heat. Because of this, Ryuga usually must defeat his opponents by the time the side effects kick in, otherwise remaining in the form for too long or immediately transforming again after being knocked out of it without letting the suit cool down will put Ryuga in danger of serious harm.
 * Evolto's Memories (Formerly): Because a part of Evolto merged with Banjo when he was still in his mother's womb, Banjo shares his memories. Banjou normally cannot recall these memories, but once Evolto attained his complete form again, he started suddenly experiencing fractions of them. Seeing memories of Evolto's destruction of Mars causes Banjo to become incredibly aggressive, to the point where he continues to attack enemies that have already been defeated and comes close to killing opponents. However, he is no longer susceptible to these memories after Sento used Genius Form to transfer Vernage from Misora's body to Banjo's, leading to Vernage's power neutralizing Evolto's effect on Banjo.

Devices

 * Build Driver - Cross-Z's transformation device
 * Fullbottles - Cross-Z's transformation trinkets
 * Fullbottle Holder - Carrier strap for Cross-Z's Fullbottles
 * Cross-Z Dragon - Slot adapter for Build Driver and personal familiar. Also utilized in Twin Breaker finishers
 * Cross-Z Magma Knuckle - Secondary slot adapter for Build Driver and secondary personal weapon
 * Great Cross-Z Dragon - Upgraded version of Cross-Z Dragon
 * Sclash Driver - Cross-Z Charge's transformation device. Destroyed by Evolto
 * Dragon Sclashjelly - Cross-Z Charge's transformation trinket. Destroyed by Evolto
 * Evol-Driver - Evol's transformation device, used while possessed by Evolto
 * Evolbottles - Evol and Great Cross-Z's transformation trinkets
 * Build Phone - Smartphone that transforms into the Machine Builder
 * Hazard Trigger - Borrowed from Kamen Rider Build in a brief usage against Kamen Rider Evol.

Weapons

 * Beat Closer - Cross-Z's personal weapon
 * Twin Breaker - Cross-Z Charge's personal weapon
 * Blizzard Knuckle - Cross-Z Magma's secondary personal weapon
 * Drill Crusher - Build's personal weapon borrowed by Ryuga
 * Safeguard Rifle - Guardian's assault rifle, stolen by Ryuga on one occasion

Vehicles

 * Machine Builder - Rider Machine temporarily borrowed from Kamen Rider Build

Ridewatch
Cross-Z Ridewatch (クローズライドウォッチ): Based on Kamen Rider Cross-Z, this Ridewatch would provide access to the Cross-ZArmor. Sento found this Ridewatch in the vortex of two worlds combining.

Friends/Team Build:

 * Sento Kiryu: In the beginning, they started off as enemies and worked together at a rocky start. But in time, they grew closer as the best of friends and brothers. But despite learning, Sento's alter ego, he never forgave him as Katsuragi for the death of his beloved. Throughout the wars with Hokuto and Seito, their bond still remained intact. Sento's been the brain, while Ryuga the brawn, as they always quarrel.
 * Misora Isurugi: Both her and Ryuga didn't get along at first, due to being a fugitive. But slowly, they connect to each other as Ryuga suffers Kasumi's death and his accusation.
 * Sawa Takigawa: Worked together.
 * Kazumi Sawatari: Both enemies once, eventually friends against Seito and later Evolto.
 * Gentoku Himuro: Both enemies as Night Rogue and later Seito's Rider Rogue, until later allies against Evolto.

Enemies:

 * Evolto: His DNA was a part of his genes, when Evolto tries to possess his mother but instead possessed Ryuga as an infant. Evolto possessed him to get his genes back, while gaining Evol Dragon.
 * Utsumi Nariaki: An enemy as Mad Rogue.

Others:

 * Soichi Isurugi: Once an ally until revealed to be Blood Stalk and the one who set up the murder of Katsuragi, until later learned he's possessed by Evolto
 * Katsuragi Takumi: Takumi was thought to have died by Ryuga's, but was actually Satou Taro's body replaced with his face altered. When Sento's memories as Katsuragi returned after being possessed by Evolto, Katsuragi saw him as an enemy related to Evolto and never treating him as a friend.
 * Emu Hojo:

Portrayal
Ryuga is portrayed by Eiji Akaso (赤楚 衛二), who previously portrayed Hiroki Nagase in Kamen Rider Amazons Season 2. Under the possession of Evolto, he is voiced by Tetsuo Kanao (金尾 哲夫).

As Kamen Rider Cross-Z, his suit actor is Eitoku (永徳), who returned in portraying "Secondary Riders" since Baron. This is Eitoku's final role to act as suit actor for Secondary Riders of the Heisei Phase 2, he is succeeded by Yuya Nawata in the succeeding season after Build. Under the possession of Evolto as Kamen Rider Evol, his suit actor is Kazuya Okada (岡田 和也).

Etymology
The kanji used to spell his first name can poetically mean "I'm a Dragon" (竜我).