Kotaro Enomoto is Natsuki Enomoto's brother, possessing a noticeable temper observed by Hina Setoguchi during a dinner at her home. Hina comments that his disposition might hinder his chances of securing a girlfriend. Kotaro harbors romantic feelings for Hina, prompting him to inquire about her to Natsuki, which triggers sibling bickering. He also teases Natsuki regarding her romantic interest in Yu Setoguchi.