Shin'ichi Gomi is a background character in Sana Kurata's sixth-grade class. Initially sporting long hair, his father forces him to shave it off upon entering middle school, earning him the nickname "Gomichhichi." When Akito Hayama stops his disruptive behavior, Gomi attempts to position himself as the new leader of the boys, trying to reignite conflicts between the girls and boys to challenge Akito's authority. Akito intends to fight him physically, but Sana Kurata, opposing violence, permits only a single punch. Akito knocks Gomi out with that punch, reasserting control.

Facing significant pressure from his parents to attend a prestigious private middle school, Gomi rebels by associating with older delinquents who previously bullied him. Together, they assault Akito, inflicting serious injuries. Gomi further descends into delinquency by shoplifting spray pistols from a store. Evading the pursuing store manager leads to Akito being wrongly accused of the theft, placing Akito at risk of expulsion and straining his family relationships.

Overcome by guilt, Gomi confesses to his father about the assault and the shoplifting. Accompanied by his father, he apologizes to the Hayama family, clearing Akito's name, and also apologizes directly to Akito himself. Later, when the same delinquents target Akito again, Gomi intervenes to protect him. Alongside Akito, Sana, and their teacher Sumirei Ando, he helps fend off the attackers using the stolen water pistols.

Gomi is frequently associated with his classmate Hisae Kamayai.