Seo is relatively normal in appearance. He has short, flat dark brown hair that goes to his nape with almond, dark eyes, a big nose, and large lips and fair skin.
Seo is a rude and arrogant person who seems to feel the need to feel superior. He is noted for having a bad personality and appears to have no qualms telling someone off.
Seo previously lived in Los Angeles for one year because of his parents' work. Because of this, his skills in English are known school-wide.
Seo is first seen with Teppei and a few other classmates walking around as he comes upon Maehara and Kaho. It is implied that Seo and Kaho are in a relationship and that he believes Kaho is cheating on him. Kaho tells him he has it all wrong and begins making excuses for why she was sharing an umbrella with Maehara. Maehara then calls her out on this as well as her behavior prior like how she hardly answered his calls anymore and switched from commuting by bike to commuting by train, and states that she'd figured she'd keep him around for when Seo is busy. Seo becomes angry at her and she claims it's not like that. She takes a moment before changing from a "guilty excuse mode" to a "full-on attack mode" and begins verbally attacking Maehara by stating that he's bad news and that they would've lost touch due to the fact that students of Class E don't advance to Kunugigaoka High School. She then tells him that she thought he would be in shock over falling into Class E and didn't clearly state that they'd broken up although she wished he would've realized it without her telling him. Seo then insults him saying that there was no way he'd figure it out with that "Class E brain" of his. Maehara tells them that that's like the pot calling the kettle black and Seo kicks him to the ground telling him that he doesn't get the situation. Him and his friends begin beating up Maehara and Seo tells him to apologize to Kaho for using the same umbrella. Chairman Asano appears and breaks up the fight. He gives Maehara his handkerchief, telling him that he is very close to being removed from the school. He then leaves and Seo and his friends say they'll overlook Maehara's "adultery" out of respect for the chairman and Kaho leaves with them saying that she had no idea Maehara was such an awful person and to never look at her again.
He is then seen with Kaho at a coffee shop. She explains the shop is owned by a friend of her father and it is very important to her. He asks if she ever brought Maehara there and she stutters while refusing that that could ever happen. They start talking about what had happened the day before. He tells Kaho to not hang out with anyone that would drop into E class. An elderly couple visit the coffee shop and ask if Seo would mind putting his leg down so they can get by. He rudely says he will and as they pass insults them to Kaho. The elderly couple is actually Nagisa and Kayano in disguises that were created by Sugaya. Sugino is then seen spying on Seo and Kaho at the cafe. After the incident that occurred the day before, E class decided to get revenge on the two by humiliating them. The disguising are said to be so effective because Seo and Kaho have no interest in weak people so they would not look closely at the elderly, The room Sugino and Sugaya are in is only available because Yada and Kurahashi are keeping the landlord busy on the first floor. Nagisa and Kayano have a conversation loud enough for Seo and Kaho to hear about going the bathroom. They talk about how there is a bathroom a hundred meters down the road at a convenient store but Nagisa tells Kayano just to use the bathroom at the cafe. After Kayano leaves to use the restroom, Nagisa pretends to spill his drink and knock everything off of his table. In the commotion Seo and Kaho are distracted. In this time Chiba and Hayami shoot laxative BB's specially made by Okuda. The BB's land inside the tea of Seo and Kaho. The couple then berates Nagisa on being so noisy. The drug takes effect almost immediately and the couple start fighting over who should be able to use the bathroom first. However, once they reach the restroom they realize the old woman from before is still inside. They then remember the conversation Nagisa and Kayano had about the other bathroom one hundred meters away and sprint towards it. On there way to the bathroom; Isogai, Maehara, and Okano are cutting down branches. The branches then fall on top of Seo and Kaho soaking them. They finally reach the rest room but are still fighting over who gets to use it first.
- Despite the fact that he's fluent in English, he cannot speak the standard dialect.
- The character book mentions that he makes everyone in Class A uncomfortable because he's so disrespectful and arrogant, yet he's so high-achieving.
- According to the Graduation Album, he and Tsuchiya Kaho end up attending the same university, repeatedly separating and reconciling.
- Recently, both have been thinking, “He/She might just be the only one for me.”
|Kunugigaoka Junior High School|
|Faculty||Korosensei • Tadaomi Karasuma • Irina Jelavić • Aguri Yukimura|
|Students||Masayoshi Kimura • Hinano Kurahashi • Yuma Isogai • Hinata Okano • Hiroto Maehara • Meg Kataoka • Kotaro Takebayashi • Toka Yada • Koki Mimura • Rio Nakamura • Nagisa Shiota • Kaede Kayano • Taisei Yoshida • Yukiko Kanzaki • Taiga Okajima • Rinka Hayami • Tomohito Sugino • Yuzuki Fuwa • Takuya Muramatsu • Kirara Hazama • Ryunosuke Chiba • Manami Okuda • Sosuke Sugaya • Sumire Hara • Ryōma Terasaka • Karma Akabane • Itona Horibe • Ritsu|
|Faculty||Gakuho Asano • Kiyoshi Terai|
|Students||Tomoya Seo • Teppei Araki • Natsuhiko Koyama • Ren Sakakibara • Gakushu Asano • Kaho Tsuchiya • Kazutaka Shindō • Kokona Tagawa • Nobuta Tanaka • Chousuke Takada|