Tanpei Kimokawa operates as a gangster in Tokyo. He meets Betty, a devil-girl, during a rainstorm and rapidly enters a relationship, moving in with her in a high-rise apartment. His gangster background shapes his behavior. Tanpei struggles to adapt to Betty's supernatural family, including witches and demons whose unexpected visits create ongoing domestic tension. His loyalty faces a test when Betty's grandmother sends nubile nymphs to seduce him, assessing his suitability as Betty's husband. This leads Tanpei into sexual encounters outside his relationship with Betty. His actions reveal a struggle with fidelity following the relationship's swift progression. Tanpei also engages in violent conflicts, notably attempting to attack gangsters with a sword, resulting in him being stabbed in the stomach. Betty intervenes to resolve this conflict. His character navigates criminal activities, supernatural family dynamics, and relationship challenges without significant development or deeper exploration of motivations, functioning primarily within the framework of Betty's mission and her familial interactions.