Mutsu is designated as Sekirei Number 05. He is one of the few male Sekirei in the series and formerly served as a member of the first generation Disciplinary Squad, also known as the S-Plan Guardians. He is a tall figure with messy silver-colored hair and gray eyes. His attire consists of dark pants and a long-sleeved black shirt left open at the front, and he carries a sword at his side. Despite carrying the weapon, he has never been seen drawing it; instead, he uses the butt of the scabbard as a blunt instrument, slamming it into the ground to generate powerful shockwaves and create large fissures, indicating that he possesses earth-based abilities.

Mutsu is partnered with the Ashikabi Hayato Mikogami, to whom he is deeply loyal and protective. He is calm, reserved, and serious in demeanor, rarely showing emotion. His motivations center on safeguarding his Ashikabi and fulfilling his role in the Sekirei Plan, even when facing powerful opponents. He demonstrates a strong sense of duty and willingness to put himself in harm's way for those he cares about.

In the story, Mutsu appears as a supporting character in Sekirei: Pure Engagement, primarily acting alongside his Ashikabi and occasionally clashing with other Sekirei. His key relationships include Hayato Mikogami, with whom he shares a bond of mutual respect, and other members of the Disciplinary Squad such as Karasuba, Haihane, and Benitsubasa. His development is mostly centered on his unwavering dedication to his Ashikabi, though he shows subtle growth in his interactions, particularly when forced to confront the harsh realities of the battle royale. Notable abilities include his earth-manipulation technique, which he uses both defensively and offensively to alter the battlefield and protect his allies.