Hayate Kanuma is the primary assassin for the Shinogara, a clandestine ninja organization secretly ruling Japan. His father leads the group, placing Hayate near its apex. Deeming the Shinogara's oppressive control unjust, Hayate commits patricide to shatter their authority. This act forces him into flight, relentlessly hunted by former allies seeking vengeance.

Near death during his escape, Hayate employs a soul-transfer technique to survive. He merges his consciousness with his younger sister, Shiori Kanuma, inhabiting her body while retaining his lethal ninja skills. This symbiosis allows Shiori to access Hayate's combat prowess when facing Shinogara threats. Each activation, however, slowly consumes Shiori's individuality, diminishing her true self.

Physically, Hayate possesses brown hair and purple eyes. His existence now relies entirely on Shiori's physical form. This shared state is a doomed arrangement, inflicting cumulative damage to Shiori's identity. Hayate's driving goal shifts: he must permanently dismantle the Shinogara to secure his sister's survival and freedom from their pursuit.

His core relationships revolve solely around his protective yet burdensome bond with Shiori and the patricide that ignited the conflict. His documented abilities are limited to soul transference and ninja combat.