Kōichi Shindō attended junior high with Izumi Miyamura and Makio Tanihara, becoming Miyamura's sole close friend during a period of isolation fueled by Miyamura's appearance and perceived demeanor. Shindō actively countered negative opinions, confronting Tanihara about the group's role in Miyamura's withdrawn state. He found Miyamura fascinating and sustained their bond despite attending different high schools—Miyamura at Katagiri High and Shindō at Yasaka High due to parental pressure for higher academics. Tall and lean, Shindō possesses medium-length, spiky orange hair typically parted on the right with a prominent cowlick, and distinctive lime-green eyes. He exhibits a consistently kind, upbeat, and smiling personality, contributing to his middle school popularity. Though initially forgetful, struggling multiple times to recall Miyamura's name correctly early on, this improved. He demonstrates seriousness regarding his relationship challenges, expressing deep distress over intense parental disapproval from his girlfriend Chika Ichijou's family. Despite this, he remains defiantly committed, vowing not to give up after reassurance from Miyamura. He requested Chika wait one year for him to graduate and improve his circumstances. His relationship with Chika Ichijou began after his confession and her immediate acceptance. Chika appears unaffected by other girls' interest in Shindō. Being one year behind academically, she promised to wait during her graduation. Shindō devoted 60% of his time to Chika. Her parents disapproved partly due to Shindō's poor academic performance, including repeating his second year of high school multiple times. Under Miyamura's influence, Chika's treatment became more forceful, such as slapping a cigarette from Shindō's mouth and collaboratively overcoming his aversion to cheese. Shindō's friendship with Miyamura remains strong across different schools, characterized by mutual regard as best friends with sibling-like closeness. They frequently visit each other's homes and know each other's parents well. Miyamura confides deeply in Shindō, sharing secrets like showing him a bite mark from Hori and likely revealing his tattoos and piercings first. Shindō allocates 30% of his time to Miyamura, knows personal details like his measurements, and understands him well. Miyamura considers Shindō his first friend and credits him, alongside Hori, for enabling him to be his true self. Shindō maintained a friendship with Makio Tanihara from junior high, though it strained when Shindō prioritized Miyamura. Tanihara later assumed a role trying to keep Shindō and Miyamura in check within their group dynamic and occasionally received tutoring from Shindō. Academically, Shindō struggled significantly at Yasaka High, repeating his third year multiple times. His poor performance persisted, mentioning at Christmas the need to repeat again. This academic record fueled Chika's parents' disdain. In the original webcomic, Shindō was depicted as a smoker, an aspect omitted in the manga adaptation.