Koichi Sumita arrives as a new student in the series' fourth season. Shy by nature, he possesses a kind and supportive personality. He harbors romantic feelings for Katie Minami, leading him to confess. His pursuit includes an orchestrated kiss, accidentally arranged by Azumi Hidaka, Hanzo, and Sazo, though Katie's existing affection for Dylan Yuki complicates his efforts. Koichi demonstrates athletic prowess, excelling in sports, and has two younger twin sisters. He shares Mirumo's fondness for chocolates, particularly Cloud Chocolate. Partnered with the fairy Papii, who actively assists his romantic endeavors towards Katie despite being unaware of Katie's feelings for Dylan, Papii utilizes a handbell as her magical instrument and matches Koichi's enthusiasm for connecting him with Katie. Recognizing Katie's persistent affection for Dylan and the unlikelihood of his own romantic success, Koichi chooses to step back. He eventually begins a relationship with Haruka Morishita, another fourth-season character. Even after shifting his romantic focus, he maintains his supportive role towards Katie.