Shun Kaidō attends PK Academy. Previously, in middle school, he was shy, friendless, wore glasses, and hid behind his hair. Entering high school, he reinvented his appearance with spiky hair and contact lenses. Meeting upperclassman Mineo Nobuaki, who has chuunibyou syndrome, inspired Kaidō to adopt grandiose delusions. He proclaimed himself "The Jet-Black Wings," asserting his right arm harbors a dark force called "Black Beat," sealed by red bandages worn constantly. He believes the evil organization Dark Reunion seeks world domination and targets him for his supposed powers. His invented backstory details Dark Reunion training the Jet-Black Wings as an assassin; the entity later betrayed them, transferring its soul into Kaidō before birth. Kaidō stands 159 cm tall with light blue spiky hair and red eyes, making him the shortest boy in his class. His modified school uniform features a tattered collar, reflecting his chuunibyou style. Outside school, he favors dark, gothic-style clothing. Despite claims of supernatural power, he is physically weak, struggles in sports, and cannot swim. His personality fluctuates between a confident, delusional front at school and a more typical, anxious teenager around his strict mother or under stress. He fabricates elaborate stories about battling Dark Reunion, often attempting to impress peers like Saiki Kusuo, usually leading to embarrassment. However, he exhibits moments of genuine courage, like instinctively shielding classmates from danger, such as jumping in front of a snake. Academically strong due to his mother's pressure, he lacks practical intelligence—struggling with navigation or misunderstanding basic concepts like hair clinics being medical facilities. Relationships are central to Kaidō. He initially sought friendship with Saiki after mistakenly believing he witnessed him teleporting; though Saiki resisted, a bond formed. His closest friend is Aren Kuboyasu, whom he addresses by first name. He is part of the school's Occult Club and becomes the romantic interest of Yumehara Chiyo after her breakup. His home life includes a mother who enforces strict studying, a younger sister (Sora), and a brother (Toki) who genuinely believes his chuunibyou stories, causing awkwardness when Toki repeats these tales publicly. Throughout his experiences, Kaidō's chuunibyou persona persists, but subtle growth occurs. He integrates more into his friend group and occasionally shows self-awareness about his fantasies. His complex self-perception includes creating seven distinct internal personalities, such as "Destructive Jin" (desiring control) and "Lawful Kai" (protecting others). Despite occasional scams exploiting his belief in Dark Reunion, his friends consistently support him. His name derives from "shunkan idō" (Japanese for "teleportation"). His favorite food is salami. His character song is "Bloody Moon." His theme during chuunibyou acts is "Judgment Knights of Thunder." A psychic classmate identified his guardian spirit as a chihuahua and his aura resembles a chipmunk's.