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) 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. 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
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. Also to be noted is that he seemingly considered destroying Smart Brain more important than Mari. He also passionately despises the Orphnochs, regardless of whether they "have souls" or not and sweared 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. Like some of the other Secondary Riders, Kusaka acted as a mean and nasty person towards the Main Rider but unlike the rest of them, he never reformed and befriend said 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. Despite being mostly unlikable throughout the series, it seems Kusaka somewhat wanted to stop the Orphnochs to save humanity although most of his reasons seemed to be for revenge.

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.

In a film-exclusive revision of Masato's death which took place towards the end of 555, 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 555 video game
Kamen Rider Kaixa is playable along with Faiz and Delta in the Kamen Rider 555 video game.

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.

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 behaviour to dust his palms is because remembering his incident from the Orphnoch's beginning attack.

Standard Equipment

 * 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).