|Height||178 cm (5'10")|
|Weight||72 kg (158 lbs)|
|Age||17[note 1][note 2]|
|Occupation||Mekakushi Dan Member No.2|
Alive (Novel Route, Mekakucity Actors, Movie)
Deceased / Inside the Kagerou Daze (Music Route, Manga Route)
|Relatives||Kenjirou Tateyama (Foster Father) |
Ayaka Tateyama (Foster Mother)
Ayano Tateyama (Foster Sister)
Tsubomi Kido (Foster Sister)
Shuuya Kano (Foster Brother)
Sayori Ishizuka (Young)
|Manga||Kagerou Daze Vol. 01, 03. Kisaragi Attention|
|Novel||Kagerou Daze II -a headphone actor- (Tsuitou Forest)|
|Anime||Act 01: Jinzou Enemy|
|“||After all, making new friends... It's spontaneous. A coincidence that happens to turn out right.||”|
Kousuke Seto (瀬戸 幸助 Seto Kōsuke) / Seto (セト) is the second member of the Mekakushi Dan.
- Seto is a tall young man with short black hair and hazel yellow eyes. He wears a green jumpsuit with a pair of goggles attached to its hood, an equally green belt and outer pockets, and dark green sneakers. He also wears a yellow hair clip on the left side of his head. His sleeves and pant legs are rolled up, showing the white inside of the suit. A black leather strap with a metal buckle on its end comes from each goggle of his hood.
- When he was young, he wore a purple button-up shirt, a white hoodie, golden brown trousers and purple sneakers.
- On August 14th in Mekakucity Actors, he wears a black shirt with a red neck underneath his jumpsuit and shoes that appear almost black. He changes to his regular outfit on the 15th.
- At the end of Summertime Record, Seto is seen wearing a yellow shirt underneath a new white hoodie, which he wears with its sleeves rolled up to his elbows, along with the pants part of his green jumpsuit. He ties the arms of his jumpsuit around his his waist during this appearance.
- In Kagerou Daze -in a day's-, Seto wears a short-sleeved green button-up shirt over a pair of dark blue (likely denim) overalls, which he wears with its bib down and legs rolled up to his knees to reveal its brown interior. He wears green socks that match his shirt and brown sneakers that match the interior of his overalls.
- Seto is a kind-hearted person that gets along well with others. When he was a child, he grew up without parents and had trouble understanding others. His only friend ended up being a stray dog, which he later tried to save from bullies. That event lead to both of their deaths and Seto's encounter with the Kagerou Daze, where he gained his eye ability. Not long afterwards, he and Kido were assigned to Room 107 of the orphanage together because their eye abilities disturbed everyone else, and Kano joined them not long afterwards. Seto, who still grieved over Hanako, frequently cried and got in trouble with Kido for speaking politely to her.
- Because he had difficulty controlling his ability, he would frequently and accidentally read others' thoughts and emotions. This continued even after he was adopted by Kenjirou and Ayaka Tateyama and became part of the Mekakushi Dan, which was founded by Ayano. One incident causes him to run from the city, which he found to be full of dishonest hatred, to the forest, where he meets Marry and, with his eye ability, learns of her loneliness. In the Music Route, he even learns of his and his siblings' deaths by the Snake of Clearing Eyes. In all Routes, he decides to befriend her and take her to the Mekakushi Dan.
- About three years before the start of the series, Seto decided that he has to become stronger and takes on part-time jobs to do so. Currently, he works as a florist at a shopping center and has other jobs, such as traffic control and delivering newspapers. Seto lives with Kido, Seto, and Marry in an apartment that also serves as the Mekakushi Dan hideout. He often wanders off to explore new places. Since learning how to control his eye ability, he has expressed disliking using it on people and will only do so when necessary. Instead, he uses it most frequently to understand animals and communicate with them.
- In the current day, he is much more cheerful and has achieved his goal of becoming physically strong. He is very loyal to the Mekakushi Dan, as he will obey Kido's commands without much hesitation and will physically sacrifice himself to protect them from danger without much hesitation. In the Novel Route, he faces extreme survivor's guilt over their deaths but pretends that nothing happened for Marry, who has also been pretending to have forgotten about them. The stress of his emotions and being reminded of his lost loved ones eventually causes him to lose control of his ability for the first time in years.
- Stealing Eyes (目を盗む Me o Nusumu): Seto's eye ability allows him to hear the thoughts of others, includes animals. However, animals cannot necessarily understand him because he cannot speak their language. When he loses control of his ability, which he often did as a child, he can hear the true thoughts and emotions of everyone, even strangers, in a wide area.  When used to its full potential, it can read a person's memories and even their experiences from past Routes.
- Kuusou Forest
- Konoha no Sekai Jijou
- Kisaragi Attention
- Yobanashi Deceive
- Losstime Memory
- Ayano no Koufuku Riron
- Otsukimi Recital
- Yuukei Yesterday
- Outer Science
- He has a pet hamster named "Hanao". Another hamster appears in Manga Route 2 that is the leader of all the animals in the forest by Marry's cottage and knows of Azami, but it is unknown if this is also Hanao in this Route.
- His favorite type of girl is someone like Yachigusa Kaoru.
- Like Kido and Kano, he is referred to with his last name rather than his first name.
- His white hoodie was a gift from Ayano when they were younger, but he gave it to Marry upon meeting her.
- He usually ends his sentence with "-ssu", a way to shorten desu, a Japanese polite copula.
- Because Seto has a lot of part-time jobs, he was designed to wear something comfortable to work around, as suggested by Sidu.
- His dog's name was "Hanako".
- Seto's designs had to be corrected the most when the anime production team presented the rough character sketches. According to Sidu, he looked like a whole new character.