Kosuke Nitoh

Kosuke Nitoh (仁藤 攻介) is the secondary rider of Kamen Rider Wizard, Kamen Rider Beast (仮面ライダービースト). He make his first appearance in the 2012 Movie War film, Kamen Rider × Kamen Rider Wizard & Fourze: Movie War Ultimatum. Referred to as "the ancient magician" (古の魔法使い, Inishie no Mahōtsukai) by the Wiseman due to his ancient Belt, he needs to absorb the mana of the defeated Phantoms in order to regain his strength.

Kosuke Nitoh
Kosuke Nitoh is a student archaeologist who is rather optimistic, often believing that pinches and chances are sides of the same coin. He discovered the Beast Driver by accident during his expeditions in ancient ruins. He also has an unusual liking for mayonnaise, constantly carrying a bottle of it with him and putting it on any food he eats, including doughnuts. Haruto and Shunpei refer to him as "Mayonnaise" because of this unique habit. When he finds Phantoms or Ghouls, he refers them as his "food" due to his ability and need to absorb Mana from them. It's shown that when Haruto finds Phantoms and tries to defeat them, Kosuke will get angry for interfering with his "feeding time". He also constantly leaves everyone around him speechless due to his tendency to interrupt others and express his thoughts without breaks.

While he sees Haruto as a nuisance, he is nevertheless willing to cure him of the poison injected into him by Manticore through the use of Dolphin Mant's powers.

Later, Kosuke revealed to Haruto, Shunpei, and Rinko that he received Kamen Rider Beast's powers from Beast Chimera. The Beast Chimera make a contract with Kosuke, granting Kosuke his magic. In exchange, Kosuke must absorb mana by defeating Phantoms and ghouls, or he will be eaten by Beast Chimera. Unlike Haruto who is knowledgeable about how Phantoms come about and operate, Kosuke initially knows nothing other than they can take human forms and he needs to eat them to survive. Later, Haruto offers Kosuke to get rid off Beast Chimera. However, Kosuke refuses and prefers if they still as eternal rivals.

Rise of Beast
Kosuke meets Haruto, Shunpei, and Rinko by chance during a Ghoul attack, when he was about to have his lunch. Kosuke is then mistaken as a Gate by Haruto. He decides to keep eye on him, much to Kosuke's chagrin, who sees Haruto's intervention to have "ruined his meal". However, the Phantom Manticore was also sent by Wiseman to attack Kosuke. Haruto transforms during the attack into Wizard to guard Kosuke, while Shunpei and Rinko takes Kosuke away from the scene.

Meanwhile, Kosuke, annoyed by the trio's attempt to keep him safe, ran off on his own and met a tarot fortune teller, whom he had taken an interest in. Kosuke then decide to let the fortune teller predict his future. The fortune teller tells Kosuke that his future is bleak, but Kosuke, due to his super positive mindset, retorts in a cheerful manner that wherever there is a danger, there is an opportunity waiting. He further irks the fortune teller by saying that even hope can be found within despair. The fortune teller is later revealed to be Manticore when Haruto arrives to save Kosuke, and chokes Kosuke as Manticore revealed himself.

Instead of feeling afraid like victims usually do, Kosuke is overjoyed instead. Due to Haruto's inability to fend off Manticore in his current state, and that Kosuke desperately "needs to feed", he transforms into Kamen Rider Beast. After making short work of the Ghouls (and devouring their magical energy), Kamen Rider Beast takes on Manticore and uses Chameleo Mant to attack the Phantom unseen and gives him a hard time.

When Haruto tries to warn Kosuke of Manticore's poison attack, Kosuke was caught off-guard and the Phantom successfully poisons Kamen Rider Beast. However, Beast uses Dolphi Mant shortly afterwards to cure himself and Haruto, further angering Manticore. Kamen Rider Beast then uses Falco Mant and overpowers Manticore, and finally finishing the Phantom off with Falco Saber Strike and absorbing his Mana.

Though greeted by Haruto over his victory, Kosuke says nothing to reveal his origins as Kamen Rider Beast, but warns Haruto in a peculiar manner to never again interrupt his "meal".

Magical Food
Kosuke was seen having his camp set up and enjoying a barbeque in a shrine, but was asked to leave by a temple elder. He then sees an artist, Hiroshi Oikawa, being attacked by the Hydra Phantom. Haruto also arrives at the scene and immediately transforms into Kamen Rider Wizard to engage the phantom. Since he was the first to spot the phantom, Kosuke is annoyed by Haruto's interference yet again, and he tranforms into Kamen Rider Beast to proceed to fight Hydra Phantom as well. Upon realisation that he has to fight two magicians at once, the Hydra Phantom decided that his chance of coming on top is too slim and escape in the midst of Wizard and Beast's bickering over who should fight the phantom. Kosuke then accused Haruto, saying that it was his fault that his "meal" escaped again.

Taking a break at the donut shop, Haruto is curious about how Kosuke obtained Beast's powers. Kosuke then tells Haruto and friends about the story regarding him and Kamen Rider Beast. Apparently some time ago, Kosuke was an archeologist who went on expedition discovering some ancient ruins. Soon, he chanced upon the Beast Driver and met the Beast Chimera, who then made a pact with Kosuke. To his utter surprise, several Ghouls were released within the cavern's vicinity, but he managed to transform for the very first time and defeat them as Kamen Rider Beast.

Some time later, Haruto is alerted that the Hydra Phantom is going to attack Hiroshi once again. On the other hand, while sending Griffin to look for the phantom, Kosuke meet Misa, who is actually trying to make use of him by lying that Haruto is trying to destroy the Hydra Phantom so that he can absorb the phantom's mana, as well as telling him that Gates have Phantoms ready to be harvested in them, though expectedly leaving out the additional detail of require the Gate in question to fall into despair and die first. Acting on impulse and choosing to believe Medusa despite her being a phantom, Kosuke rushed to the scene of battle quickly to stop Wizard. While Wizard in his Water Dragon form is engaging the Hydra Phantom, Kosuke then transforms into Kamen Rider Beast with Buffalo Mant in an attempt to stop the battle. In the midst of the skirmish, Kosuke wants to know which side, Wizard or Phantom, can offer him a better deal in providing him the mana of phantoms.

Today's Life, the Life of Tomorrow
After battling Wizard Water Dragon, Kamen Rider Beast decide to retreat, but he kidnapped Hiroshi also. Kosuke then asks Oikawa how to to leash his inner Phantom. However, Oikawa leaves as he had no idea what Kosuke is referring to. In spite of that, Kosuke still accompanies Oikawa to his home. At Oikawa's home, Kosuke found out that the source of Oikawa's hope is his portrait of his late wife. Since his wife had passed away, Oikawa had stopped drawing due to the lack of encouragement. A moment later, Haruto, Rinko and Shunpei reached Oikawa's home. Kosuke then meet Haruto, who told him that Gates are not merely Phantom lures. Instead, they are humans with magical potential, and can be turned into Phantom if they fall into despair. Kosuke was dumbfounded by this, as he must keep eating Phantoms that conflicted with what gates are. However, sacrificing a human to become the Phantoms will leave a bad after taste.

Later, Rinko and Shunpei proceeds to move Oikawa's wife picture to a safer location for fear that a Phantom may destroy his source of hope. On their way, they encountered Hydra Phantom and Ghouls. Rinko and Shunpei are helpless against the numerous Ghouls, as one of them took the opportunity to grab the picture. Hydra Phantom then destroys it in order to let Oikawa fall into despair. However, Kosuke arrives in fashion with a flying kick on one of the Ghouls. Kosuke then transforms into Kamen Rider Beast, and Haruto arrives and also changes to Wizard. The two then use Buffa Mantle and Land Style respectively to defeat the Ghouls. Wizard then decides to let Beast to take care the Underworld Phantom, while he battle Hydra Phantom. While Wizard Land Dragon defeats the Hydra Phantom, Beast encounters Bandersnatch Phantom in Oikawa's underworld. Kamen Rider Beast tried his best to defeat the Underworld Phantom, but then it became apparent that he is not so strong enough to do it alone. Hence, Beast summoned Beast Chimera, which overpowered the Bandersnatch Phantom with much effort. Beast Chimera then defeat the Underworld Phantom using its finishing attack.

Kosuke then meet Haruto, who thanked him for helping to defeat the Underworld Phantom. Haruto then offers Kosuke to get rid off his inner Phantom, the Beast Chimera. However, Kosuke refuses the Engage Ring at last second for two reasons. First, it is very awkward if a man takes a ring from another man. Second, Beast Chimera is very strong, it will leaves a bad after taste if Haruto dies battling his inner Phantom. In addition, Kosuke prefers staying as Haruto's eternal rival. However, the question is how long will Kosuke lives.

Beelzebub Plans & Dragons' Wild Dance
On a windy night, Kosuke walks in a bridge and enter a ramen shop. However, Kosuke still doesn't eat any Phantoms. Kosuke then try to put his mayonnaise to the ramen, but he has hard time to do it, even at eats the ramen. When Wizard fights Beelzebub, Kosuke joins the fray for eating some Ghouls. Kosuke then change to Beast and use Chameleo Mantle to defeat all Ghouls. He then use Buffa Mantle to very easily handle the Ghouls. However, when Wizard Flame Dragon deliver an attack to Beelzebub, it always counter for Beast. The attacks keep injuring Beast and annoy him. After Wizard Flame Dragon defeated, The White Wizard easily dispatched Beelzebub. White Wizard then states that Beast is archetype Wizard. Soon the White Wizard disappear, before Beast could deliver any questions. As Rinko informed, Beelzebub control peoples with his slugs. Kosuke and Shunpei rush to destroy the slugs. However, destroying the slugs are useless. Kosuke then battle Beelzebub as Beast again, but easily overpowered. However, Haruto arrives with Drago Timer to summon the Dragon Styles clones. Soon Beelzebub easily defeated by Wizard Dragon Styles.

Super Hero Taisen Z
Beast is set to appear in Kamen Rider × Super Sentai × Space Sheriff: Super Hero Taisen Z, where he fights Space Sheriff Sharivan.

Mantles
Unlike Wizard, Beast doesn't use alternate forms to combat the Phantoms he consumes. Instead, he uses single shoulder mantle armaments called Mantles (マント, Manto) to help him gain an advantage over his foes.

Kamen Rider Beast's ending theme is entitled "BEASTBITE".

Devices

 * Beast Driver - Transformation device
 * Dice Saber - Kamen Rider Beast's weapon.
 * Beast Colors - Gives access to Beast's mantle changes.
 * Griffin PlaMonster - Kamen Rider Beast's familiar.
 * Mirage Magnum - Kamen Rider Beast Hyper Style's weapon.

Portrayal
Kosuke Nitoh is portrayed by Tasuku Nagase (永瀬 匡).

As Kamen Rider Beast, his suit actor is Jun Watanabe (渡辺 淳), which the role he reprises first in Movie War Ultimatum. This is his first secondary rider role. He is also Phoenix's suit actor.

Trivia

 * He is the first secondary rider to be colored gold, and the fourth in general after Agito, Odin, and Caucasus.
 * He is similar to Kamen Rider OOO in his Latorartar Combo, as they both are yellow/gold in color and have a lion motif.
 * Him using a Griffin as a PlaMonster is probably alluding to how Griffins have the body of a lion.
 * Beast's relationship to Beast Chimera is similar to the relationship with the Kamen Riders from Kamen Rider Ryuki and their Contract Monsters.
 * Beast's ability to absorb mana from the Phantoms echoes Beet and Stag Buster, the additional heroes of Tokumei Sentai Go-Busters, the first Super Sentai show that Wizard aired alongside, whose respective mechas (BC-04 and SJ-05) are able to siphon Enetron from Enetron tanks and Vaglass MegaZords.
 * His unsual liking to mayonnaise is similar to Toshiro Hijikata from Gintama.
 * Kosuke is the second individual to be mistaken as a Gate after being attacked by Phantoms (obviously, he's actually a full wizard), the first was Satoshi Ishii from episodes 14 and 15 who was revealed to be the Phantom Lizardman, the real Satoshi having perished when Lizardman was released along with the other Phantoms in the Sabbath.
 * According to Kosuke's actor, he wanted to call the Phantoms "Yummies" because of how Kosuke eats their mana, but the director told him no, in order to avoid confusion with the monsters of Kamen Rider OOO.
 * In his Hyper Style, Beast is almost similar to Ryukendo.