Tomoya Seo

Seo comes across as ordinary in looks. His dark brown hair is short and flat, falling to the nape, and it frames narrow dark eyes set above a large nose and full lips. His complexion is fair.

Abrasive and full of himself, Seo carries a constant need to look down on those around him. He is widely regarded as having a genuinely unpleasant character and shows no reluctance about berating people to their faces. A year spent in Los Angeles for his parents' work gave him English skills that are known across the school, and that talent only feeds his arrogance, though notably he cannot manage the standard dialect. The Character Book notes that even his own Class A finds him hard to stomach, unsettled by how rude he is despite his high achievement.

Seo appears alongside Teppei Araki when they stumble on Hiroto Maehara sharing an umbrella with Kaho Tsuchiya, whom Seo is implied to be dating. Convinced she is cheating, he listens as Maehara exposes how Kaho had been stringing him along, then joins his friends in beating Maehara down and demanding an apology. Chairman Gakuho Asano breaks up the assault and warns Maehara he is close to expulsion, after which Seo and Kaho depart claiming the moral high ground.

His cruelty invites payback. Seen later insulting an elderly couple at a cafe, Seo fails to realize they are Nagisa Shiota and Kaede Kayano in disguises crafted by Sosuke Sugaya. Class 3-E, out for revenge over the earlier beating, orchestrates an elaborate scheme: Toka Yada and Hinano Kurahashi distract the landlord while Ryunosuke Chiba and Rinka Hayami slip laxative pellets, made by Manami Okuda, into the drinks of Seo and Kaho. The pair are soon reduced to a frantic, humiliating scramble for a restroom, doused by falling branches along the way. The Graduation Album reveals that he and Kaho later attend the same university, splitting and reuniting again and again, each quietly wondering if the other is truly the one for them.