Reiji Namakemono (owner)
Shadōmasutā is the spirit of Reiji's Zanpakuto.
Shadōmasutā appears as a shadow creature that resembles a wolf. His eyes are pure white while the rest of his body is jet black.
Shadōmasutā's behavior is the exact opposite of Reiji's. Where Reiji would prefer to avoid a fight if possible, Shadōmasutā wants to get in the middle of one. These conflicting personalites often lead to many arguments between the two. Despite everything though the two work rather well together.