Masato Kusaka

Masato Kusaka was a member of Ryusei School who was capable of wearing the Kaixa Gear without disintegrating afterwards and the Gear's primary wearer as Kamen Rider Kaixa (仮面ライダーカイザ, Masked Rider Kaixa).

(Source: Kamen Rider Wiki)

Ever since being killed and revived by the Dragon Orphnoch, Kusaka had a history with Orphnochs which fueled his hatred for them. While originally acting friendly towards Takumi Inui, he eventually showed his true colors and his motives were revealed.

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).

Kusaka 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. Despite disliking Kusaka's attitude, Takumi showed sorrow for him, understanding that he was in a sense, also a victim of misfortune.