Kotaro Fuma is a ninja of the Fuma clan who serves the Hojo clan throughout the Samurai Warriors series. He acts as a cryptic advisor to Hojo Ujiyasu, often recommending ruthless courses of action that Ujiyasu weighs but generally chooses not to follow. Kotaro is driven by a profound fascination with chaos. He seeks to perpetuate conflict on the battlefield, viewing the turmoil of war as a source of endless entertainment. His personal motivations remain deliberately obscured, positioning him as an unpredictable wild card within any alliance.

This chaotic philosophy sets him against characters who fight for order or specific loyalties. His foremost rival is Hattori Hanzo, a disciplined ninja of the Tokugawa clan whose commitment to duty contrasts sharply with Kotaro's love of disorder. In a pivotal event, after successfully capturing Tokugawa Ieyasu, Kotaro murders his own temporary ally, Takeda Shingen, to prevent the conflict from reaching a peaceful resolution and to ensure the violence continues.

Kotaro possesses a wide range of combat abilities. He wields oversized, clawed gauntlets that can extend like tentacles to strike enemies at a distance. True to the meaning of his clan name, Fuma, which translates to wind demon, his fighting style incorporates supernatural elements. He can summon dark flames and conjure blades of shadow to overwhelm his opponents. He relies on incredible speed and agility in battle.

His role as an advisor makes him a cynical and often silent presence within the Hojo forces. In Samurai Warriors 4, this role is expanded, where he acts as a direct counterpart to Ujiyasu, observing his lords moral struggles with detached amusement while serving as a voice for ruthlessness. His appearance is deliberately intimidating, built around a large, imposing frame and a masked face that reinforces the demonic reputation of his clan.