Sadahiro Mibu runs the small teahouse Partneon, cultivating a deliberately lazy and indifferent public persona. He frequently lounges on the couch watching television, drawing sharp reprimands from his employee, Akira Tooka, which he largely ignores. He employs Ouri Kagami part-time, fostering a trusting relationship and offering a listening ear for Ouri's problems.

Unbeknownst to Ouri, Sadahiro is a covert operative for the secretive Buddhist Kougon Sect, which combats supernatural entities called Shikabane. His role extends beyond typical Sect duties; alongside his Shikabane Hime partner, Akira (posing as his waitress), he holds unique authorization to eliminate humans when necessary. Their joint missions also target rogue Shikabane Hime who have lost their Contracted Monks.

Within the Kougon Sect, Sadahiro wields the strongest "Zadan Technique" among the monks, referring to their specialized magical abilities. He maintains a consistently aloof and pragmatic demeanor, rarely showing emotional conflict even when confronting former associates. This is most evident in his ruthless mission to eliminate Akasha, a former friend linked to Keisei Tagami; he refuses any interference or competition in the pursuit.

His relationship with Akira blends professional reliance and contentious familiarity. She openly criticizes him and uses physical reprimands, like hitting him, to curb his remarks or behavior. Despite this friction, they function as an effective team, leveraging their teahouse cover while executing hazardous assignments for the Kougon Sect.