Fuuma "Evil-wind" Kotaro, the fifth head of his clan, inherits a leadership name passed through generations. His origins result from deliberate clan breeding to forge the ultimate shinobi, incorporating foreign ancestry and oni bloodlines to enhance his capabilities. This heritage manifests in red eyes, pale skin, and red hair often obscuring one eye, alongside a height of 158 cm and weight of 49 kg. He historically served the Houjou daimyo during Japan's Warring States period, his actions helping solidify their Kanto region control. His tactics featured night raids, espionage, and psychological warfare—infiltrating enemy encampments with subordinates to spread chaos via arson, theft, and targeted assassinations. Operations like forcing the Takeda army's retreat cemented his notoriety into the Tokugawa era. As an Assassin-class Servant, his primary role revolves around sabotage and support. He wields high-level ninjutsu for intelligence gathering, combat, and evasion, generating illusions, fire, explosions, and physical clones. His Noble Phantasm, "Immortal Chaos Brigade," summons 200 spectral subordinates to engulf enemies in darkness, inflicting psychological terror and moderate damage while applying debuffs like skill sealing through "Disorder" status. A secondary Noble Phantasm, "Ogre Trance," remains sealed; it would temporarily amplify his parameters by tapping into his oni lineage at the cost of self-destructive backlash. Personality-wise, he exhibits a dichotomy: though biologically engineered for shinobi perfection, he possesses a compassionate and introverted nature ill-suited to violence. He prefers tranquility and often isolates himself off-mission. Despite his Chaotic Evil alignment, he follows orders pragmatically, prioritizing mission efficacy over moral distinctions. He reacts fiercely to perceived slights against the Fuuma clan's reputation, especially comparisons ranking them below Iga or Koga ninja. His relationships reflect his background: he reveres Sakata Kintoki as a "great senior," shares mutual respect with Hassan of the Cursed Arm over their demonic connections, and harbors unresolved bonds with Katou Danzou, referenced as a maternal or mentor figure despite no direct meetings. He also expresses regret for unspecified past actions involving Jeanne d'Arc Alter Santa Lily. During events like the Onigashima incident, his oni heritage enables manifestation in the singularity. He initially observes other oni to study their behavior, hoping to unlock his sealed Noble Phantasm, but becomes overwhelmed until rescued by allies. There, he provides tactical reconnaissance, identifies enemy weaknesses, and participates in guardian oni battles, utilizing his Noble Phantasm for diversions.