Masato Kusaka

"You survived because of me. So having you die so I can live... Is just natural. I'll live... for "your" sake too."

- Masato's spirit trying to convince Faiz to give up.

Masato Kusaka (草加 雅人) was a member of Ryusei School who was apparently absent from the reunion, but signed the autograph card. He was the only Ryuseiji who was capable of wearing the Kaixa Gear without disintegrating afterwards and as such is the Gear's primary wearer. As a child, Masato was often bullied and alone with only Mari Sonoda as his friend. Through his childhood, he falls in love with Mari, though his feelings were not reciprocated back.

Personality
When he was child, he was a crybaby and often to be helped by Mari, the reason of his desire of love to Mari. After the murder attempt on his classmate by Orphnochs, he developed a personal vendetta against them. However, his vendetta is not pure or just, as he will involve anyone to be in a dangerous position so he can gain the best advantage to destroy an Orphnoch.

In general, Kusaka is calm and polite towards everyone, except for Takumi. This, however is a guise to his true nature that even Takumi himself can see, he shows his true colors as a selfish, vindictive, and skilled manipulator who has no qualms of driving a wedge between Takumi and those around him like Kiba so he can have Mari for himself. With his twisted personality, he loves to betray anyone as long as he achieves his goals and doesn't seem to regret it, no matter the outcome. He will join any physical routine for testing his strength and often to lap his palms. His behavior to dust his palms is because remembering his incident from the Orphnoch's beginning attack, as such his hatred towards Orphonchs is so fanatical beyond belief, to the point he preys on the likes of Sawada or Takumi (who is also revealed to be one), regardless of whether they "have souls" or not and swore to destroy them all out of spite. Unlike his foil, Takumi, whose reasons of fighting Orphnochs for the sole purpose of protecting humanity, Kusaka's reasons are all motivated with petty vengeance.

Like most Secondary Riders that came before and after him, Kusaka starts off hostile towards the main protagonist, but unlike the rest of them, he continues to remain as a nasty and spiteful person and refused to befriend the main Rider. While this is somewhat understandable due to his past, it should be noted that Takumi tried to understand his pain and help him despite being treated cruelly by Kusaka thus mostly making this moot. It is also notable that Kusaka spent a great deal wallowing in self pity while stating that others such as Takumi wouldn`t understand his pain despite Takumi trying to understand said pain showing hypocrisy.

His cruelty towards every Orphnoch in the series is his fatal flaw, he refuses to determine of the alignment of other Orphnochs between good and evil and is deadset to eliminate them without second thought, it eventually lead to his karmic death at the hands of Kiba.

In Kamen Rider Zi-O, it is shown that Kusaka is not completely bereft of any positive and empathic qualities. As a result of a time paradox due to the creation of Another Faiz, and the fact that said Another Rider tried to keep his significant other alive, he is more willing to kill Karin out of mercy to relieve her of the life imposed to her by Sakuma. However, this doesn't change with the fact that his hostile relationship between him and Takumi is still intact.

History
As stated above, Kusaka had a history with the Orphnochs which fueled his hatred for them. While originally acting friendly towards Takumi, he eventually showed his true colors and his motives were revealed.

Masato Kusaka is the only one to have worn all three of the Kamen Rider belts (Faiz, Kaixa and Delta). He wore the Faiz Gear to trick Yuji Kiba. He wore the Delta Gear to battle the Beetle Orphnochs (Rhinoceros and Stag).

Masato had a great deal more Orphnoch DNA implanted into him, allowing him to use the Kaixa gear safely for a time, but near the end of the series, it began to wear off, and using the Kaixa Gear was becoming increasingly harmful to him. In the end, his neck was snapped by Yuji Kiba, who claimed the Kaixa Gear as his own towards the end of the series and dies after all of his Orphnoch DNA ran out causing himself to disintegrate into dust with Takumi and the others being unaware of his death until later when his picture of a young Mari was found. This caused Takumi`s anger to intensify as he cursed all Orphnochs including himself.

Paradise Lost
In the alternate reality movie Kamen Rider 555: Paradise Lost, Masato was killed by Leo. Keitaro Kikuchi briefly wore the Kaixa Gear by drinking the experimental transformation elixir, 'Transform 1-Shot' (変身一発) and killed the Lion Orphnoch. Due to the elixir, Keitaro was unharmed. However, when the formula ran out, the Kaixa Gear disintegrated instead.

Fighting Decade
In Decade, Kaixa is a wildcard Kamen Rider who attacks Decade after he is taken to another world by Kiva-la. He is under the impression that Decade is a hindrance to his own agenda and seeks to take the Decadriver from him. He eventually concedes when Decade is returned to the World of Kiva.

Rider War
Kamen Rider Kaixa reappears briefly in later airings of the series finale, using his Side Basshar to attack Decade and Wataru's group. He is seemingly killed in the chaos afterwards alongside many other Riders. In Kamen Rider Decade: The Last Story, Decade is shown to hold a Side Basshar card, labeled as a Kaixa card. Kaixa was presumably restored with all the other Riders after the destruction (and subsequent revival) of Decade ended the Rider War and the worlds were restored, though how he was still alive in the first place considering his fate in 555 is unclear.

OOO, Den-O, All Riders: Let's Go Kamen Riders
Kamen Rider Kaixa was part of a group of reinforcement riders led by Akira Date/Kamen Rider Birth to aid the primary riders in defeating the Rock Great Leader. All the Kamen Riders got on their bikes and performed the All Rider Break attack which destroyed the Great Leader.

Kamen Rider Taisen


"Why... Why does someone as hollow as you with nothing to protect get to live? Why do I have to die?!"

- Masato curses Takumi before he dies.

At an unknown point of time, he as Kaixa were fighting the Horse Orphnoch, however he got himself killed while Faiz battled the Arch Orphnoch. Overpowered by the Horse Orphnoch and getting knocked out of his transformation, the Horse Orphnoch then threw a fireball at him to finish Kusaka off. Desperately reaching for the Kaixa Gear, he couldn't move anymore due to his burns and injuries. Faiz went to his side with Kusaka complaining on why Faiz survived while he had someone to protect. Crying out for life, he disintegrated.

Years later, while the Kamen Riders were fighting Badan, Masato's spirit appeared before Faiz and taunted Takumi into his feelings of guilt, having the Rider interfere with Wizard and X. However Keisuke and Haruto convinced him to move on as the spirit started to disappear.

Kamen Rider Zi-O
Because of the timeline had changed, Masato was still alive in 2018. He was first seen about to kill Karin Yamabuki, but the latter was stopped by Tsukuyomi. He soon followed Tsukuyomi and Karin, proceeding to kill again but was stopped by Takumi.

It was later revealed that Masato was asked by Karin to kill her for stopping Sakuma's doing on killing the girls with the same birth and age as her, including that she and Sakuma are his friends at the same school. Masato was actually trying to stop Sakuma instead of killing Karin, but as he was no longer Kamen Rider Kaixa, he had no chance and was about to be killed until Takumi came to him.

Kamen Rider 555 video game
Kamen Rider Kaixa is playable along with Faiz and Delta in the Kamen Rider 555 video game.

Kamen Rider Battride War
Kaixa is introduced as one of NPC allies character.

Kamen Rider Battride War II
Kaixa is one of selectable summonned assist only Riders in Kamen Rider: Battride War II.

Kamen Rider: Battride War Genesis
Kaixa made his playable debut in Kamen Rider: Battride War Genesis.

On September 13, 2015, Kohei Murakami announced that he reprise his role as Kaixa in this video game onwards.

In this game, Kaixa's default playstyles is one of the well-round character to pick. However, when using his unique limited power up called Cursed Belt Mode, Kaixa sacrifices a small half of super meter in 20% (Starting Level) > 15 (Level 25) > 10% (Level 30 onwards) each level ups to utilize a powerful version of his special moves. He can also activate Cursed Belt Mode while during a normal attack string combo before performing a certain special move.

Due to Kaixa not having a final form, he is rides SB-913V Side Basshar Battle Mode as his final mode. Like Kamen Rider Birth Day in this final state, Side Basshar Battle Mode also cannot jump or guard unlike in TV series for some reason, as well as sacrifices amount of super meter when using Transportation Mode or Tag Partnered Double Rider Kick.

Arsenal

 * SB-913B Kaixa Driver - Kaixa's transformation device.
 * SB-913P Kaixa Phone - A sideflip "swing" cellphone device.
 * Kaixa Mission Memory - A small metallic card key containing the information of the Kaixa Armor.
 * SB-913C Kaixa Shot - Digital camera-shaped knuckle-duster.
 * SB-913B2 Kaixa Pointer - binocular-shaped pointer which enables to produce an energy drill deathblow.
 * SB-913X Kaixa Blaygun - A special weapon that is both a pistol, a dagger and a lightsaber.
 * SB-913V Side Basshar - Kaixa's sidecar motorcycle that can transform in a robot-like Battle Mode.

Portrayal
Masato Kusaka is portrayed by Kohei Murakami (村上 幸平). As a child, he is portrayed by Yusuke Ito (伊藤 祐介). He later portrayed in . As Kamen Rider Kaixa, his suit actor was Makoto Ito (伊藤 慎).