Ryuusuke Fujiwara is a Japanese male with ochre hair and green eyes. The murder of his family by entities called Chimeras drives his relentless pursuit of revenge. This resolve solidified when his older sister, Misa, sacrificed herself during a Chimera kidnapping attempt to ensure his escape.

Ryuusuke possesses the Ruin Arms, powerful weapon systems manifesting as combat-enhancing armor. However, only women can wield these artifacts. He strategically forms alliances with female warriors capable of using the Ruin Arms against the Chimeras, who seek to reclaim their own creation. Key allies include Mikoto Enjou, wielder of "Soul Eater," and Lin Kaifon, wielder of "Brain Jacker," both bearing similar traumas from losing family to Chimera attacks.

His first encounter with Mikoto happens during a Chimera assault, forcing her transformation into Soul Eater to protect him. Witnessing her subsequent defeat and assault by the Chimera Byakko deepens Ryuusuke's sense of powerlessness and fuels his determination. Later conflicts involve Lin Kaifon, captured and tortured by the Chimera-affiliated Pegasus using aphrodisiacs and bondage in an attempt to extract her Ruin Arms technology, underscoring the constant peril faced by his allies.

Ryuusuke operates by gathering and coordinating Ruin Arms wielders, building a defensive network against the Chimeras. His leadership is fueled by the dual objectives of avenging his family and protecting his allies, though their recurring capture and exploitation highlights the persistent threat they endure.