Masato Kusaka

  Masato Kusaka (草加 雅人) is a member of Ryusei School who was apparently absent from the reunion, but signed the autograph card. He is the only Ryuseiji who was capable of wearing the Kaixa Gear without disintegrating afterwards and as such is the Gear's primary wearer.

Masato Kusaka
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.

As children, Mari often saved him from bullies and as a result he has fallen in love with her and is willing to go to elaborate lengths to eliminate any obstacles between him and her. Jealous of Takumi's closeness with Mari and seeing him as an obstacle, he will stop at nothing to damage Takumi's standing, and as a skilled manipulator, he often secretly plays Takumi and Kiba against each other so Takumi will have no allies. However, he passionately despises the Orphnochs, regardless of whether they "have souls" or not and swears to destroy them all. His hatred was driven by the events that took place at the Ryusei School reunion and he continually wipes his hands to remove the imagined blood he remembers from that night.

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).

Paradise Lost
In the movie Paradise Lost, Masato was killed by Leo (possessor of the Psyga Gear). Keitaro Kikuchi briefly wore the Kaixa Gear by drinking the experimental henshin elixir, 'Henshin 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
to be added

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

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 Kamen Rider Kaixa, his suit actor was Makoto Ito (伊藤 慎).