|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||03. Kisaragi Attention|
|Novel||Kagerou Daze II -a headphone actor-|
|Anime||Act 01: Jinzou Enemy|
|“||It's such nice weather. But I wonder where this is. There's a deer I've never seen before.||”|
Kousuke Seto (瀬戸 幸助 Seto Kōsuke) / Seto (セト) is the second member of the Mekakushi Dan.
- Seto is a young man with short black hair and hazel eyes. He wears a dark green jumpsuit with a pair of goggles attached to the hood, a brown belt, 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.
- When he was young, he wore a white hoodie with golden trousers and purple sneakers.
- In Mekakucity Actors, he wears a black shirt with a red neck underneath his suit and shoes that appear almost black.
- In Summertime Record, Seto is seen wearing a yellow shirt underneath his white hoodie, along with the pants part of his green jumpsuit.
- Seto is a kind-hearted person and gets along with everyone. He is also close childhood friends with Kido and Kano, as they all came from the same orphanage, and later, Seto lives with them together in an apartment. He often wanders off to explore new places. To earn money, he works as a florist at a shopping center and has other jobs, such as traffic control and delivering newspapers.
- He dislikes his Eye Ability and rarely uses it on people. He first discovered his ability to understand the speech of animals while wandering through the forest before he ran into Marry.
- Stealing Eyes (目を盗む Me o Nusumu): Seto's eye ability which allows him to hear the thoughts of his target's mind, which includes animals. However, even though he is able to understand animals, the animals cannot understand him because to them he still speaks human 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. 
- 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". The hamster may know something about eye abilities, as he calls Seto a monster. It also appears to know about Azami.
- 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 is "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.
- "Encounters are produced through coincidences." ( To Marry in 23. Kagerou Daze VI )
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