Tamotsu, known as Mokkun, is a white-collar worker and frequent patron of Bebe, a beachside bar run by Pico's grandfather. While his specific occupation remains undisclosed, his affluent lifestyle is evidenced by possessions like a new car and a spacious apartment. During a summer visit to Bebe, he encounters Pico working there. Mistaking Pico for a girl due to his feminine appearance, Tamotsu initiates a seduction. Even after discovering Pico is male, he continues pursuing a sexual relationship.

Tamotsu later presents Pico with feminine clothing, including a ruby choker and panties, and persuades him to wear the items despite initial reluctance. Within this relationship, Tamotsu assumes the dominant role ("seme") and primarily treats Pico as a sexual object. This dynamic causes Pico emotional distress, particularly when Tamotsu avoids defining their relationship, prompting Pico to cut his hair and flee. Tamotsu subsequently searches for Pico, displaying genuine concern during his absence. The two eventually reconcile. Tamotsu does not appear in later installments of the series and is absent from narratives beyond the first original video animation and its edited version, with no further development or involvement in Pico's subsequent relationships.