Seri Koyuki is a high school student determined to preserve a normal and peaceful school life, a goal consistently disrupted by his eccentric classmate, Kabuto Hanadori. Kabuto believes himself to be a destructive god and insists that Seri is his reincarnated comrade, Gestöber.

Seri has a cat-like appearance, marked by two tufts of hair resembling cat ears and a belt that often swings like a tail. This complements his personality, which is similarly feline—easily annoyed and keen on avoiding unnecessary attention. Despite his attempts to remain detached, he often becomes overwhelmed by absurd situations instigated by Kabuto and Utsugi Tsukimiya, who enjoys manipulating events to provoke reactions.

Academically diligent, Seri nevertheless scores lower than peers like Kabuto and Utsugi, a persistent source of frustration. Group activities such as study sessions frequently devolve into chaos due to his classmates' antics, undermining his focus. Kabuto occasionally outperforms him in certain subjects, adding to his irritation.

In interactions, Seri often appears irritable and dismissive, reacting with anger or violence toward those who disturb his peace. Yet beneath this exterior, he shows care and concern for his classmates, even if reluctant to admit it. He sometimes worries about their well-being when they are not bothering him, suggesting hidden depth.

A defining trait is his role as the rational observer amid chaos. He frequently monologues about the absurdity of his surroundings, explaining ridiculous situations in a way that underscores his logical nature but sometimes dampens comedic effect. This tendency to critique often leads to further frustration.

Seri’s background includes mentions of his mother and father, though details about his family life are sparse. He also has a childhood friend, Kimikage Mogami, who exhibits some of the same chuunibyou traits that Seri finds irritating, complicating his social dynamics.

He experiences minor developments, such as moments of self-reflection where he recognizes his own flaws and the consequences of his actions. After embarrassing incidents, he may attempt to make amends, though these efforts are often thwarted by further misunderstandings. Over time, he shows reluctant acceptance of Kabuto and Utsugi’s presence in his life.

His relationship with Kotoko Sumiso, a kind-hearted classmate, stands as one of his few positive connections. He admires her and tries to clear misunderstandings caused by his dealings with Kabuto, demonstrating a desire for genuine relationships. These attempts are often interrupted by Kabuto’s interventions or Utsugi’s manipulations, leading to comedic yet frustrating outcomes.

In his personal time, Seri enjoys playing online games as an escape from school chaos. However, even this refuge is invaded by Kabuto and Utsugi, who also play the same game, blurring the line between his desired solitude and unavoidable social entanglements.

Despite ongoing struggles, Seri does not undergo drastic change but gradually acknowledges his circumstances. He remains caught between a desire for normality and the relentless weirdness of his environment, embodying the tension between conformity and chaos.