Mayuta Andō, once the leader of a motorcycle gang, undergoes a drastic change after Chio Miyamo accidentally topples him from his bike. During this encounter, Chio adopts her online persona "Bloody Butterfly" in a panicked attempt to escape, inadvertently intimidating him. This event spurs him to abandon delinquency for an honest job as a convenience store clerk.

He develops romantic feelings for Chio and consistently attempts to win her affection through exaggerated or absurd gestures. These include dramatic confessions and misguided actions, such as performing scenes from a BL game under the mistaken belief she would enjoy the reference, leading Chio and Manana to briefly question his sexuality. His romantic efforts culminate in two key confessions: an initial, unclear declaration in chapter 33 misinterpreted by Chio as a comment about a "life buoy," and a direct, clear confession in chapter 43, which she reciprocates, making them an official couple.

His younger sister, Chiharu Andō, deeply admires him and is determined to find the woman responsible for his reform. Initially convinced Manana Nonomura is "Bloody Butterfly," she eventually discovers Chio's true role. Mayuta demonstrates protective instincts toward Chiharu, notably defending her against Manana even while unconscious.

The characters in his name, combining "cocoon" (繭) and "thick/great" (太), alongside his surname meaning "peace/quiet" (安) and "wisteria" (藤), contrast with his former delinquent identity and subtly reflect his transformed life.

Throughout his development, he maintains contact with former gang members while adapting to his new routine. His storyline emphasizes personal growth, shifting from gang leadership and confrontation to comedic efforts in retail and earnest romantic pursuits, all while navigating his responsibilities as an older brother.