Mutsuki Ashiya serves in the Yamainu Squad, a covert unit combating supernatural threats. His striking gray hair and golden eyes are accentuated by a pink scarf habitually draped over his mouth, concealing both a birthmark and intricate tattoos that channel his magical prowess. A practitioner of onmyoudou, he summons twin female shikigami for reconnaissance and wields a longsword with lethal precision. The hidden tattoos enable him to fracture an opponent’s will—a ruthless interrogation tactic.

Born into the Ashiya lineage, guardians of the Orochi’s vessel, his childhood fractured when his mother abandoned their heritage, leaving him estranged and emotionally detached. Despite a flirtatious exterior, he maintains unwavering loyalty to the Yamainu and its leader, Abe no Sosei, setting aside ancestral tensions between their families. His bonds include a surrogate parental tie to Taiko Kumo, who offered stability absent in his youth, and a protective devotion to Botan, whose compassion mirrors the maternal warmth his family denied him.

A gnawing fear of becoming the Orochi’s vessel haunts him—the dread of destroying what he cherishes—reinforcing his preference for detached observation over emotional ties. When suspicions arise regarding his loyalties due to his bloodline, he reaffirms his commitment to the Yamainu, prioritizing duty over past conflicts. His evolution balances pragmatic detachment with unspoken protectiveness, shaped by familial scars. Interactions with allies like Sosei and Botan reveal a guarded resolve to shield others while resisting deeper connections, embodying a life tethered to duty yet wary of its costs.