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Appearance
As a child, Yuuichi had scruffy, short black hair. As he got older, he began to grow it out more and now has longer bangs.

Child Yuuichi tended to wear a regular t-shirt. During the various versions of Tomodachi Game, older Yuuichi has either worn his high school uniform (Secrets Game - Shibe's trial), the uniform of the game (Prison Game), or a long black jacket over a t-shirt and pants (all other periods).

Yuuichi is relatively tall and fairly lanky. Facially, Yuuichi has some of the sharpest features in the series, with his jaw, eyebrows, and eye shape all being well-defined. He also has some of the most varied expressions. When having touching moments with his friends, he has shown softer and more happy faces. However, he has an insane slasher smile that is often brought out when he gets serious in a game.

Personality
At the beginning of the story, Yuuichi appears to be a diligent and happy student, who works hard to be able to join his friends on the school field trip. He values his friends heavily throughout the story. He shows kindness and a willingness to self-sacrifice for the sake of his friends, even going so far as to brand himself the traitor in order to prevent further discord.

As the story progresses and the games become more and more serious, however, Yuuichi begins to show a much more sinister side. This dark nature is likely the result of his troubled upbringing by an adopted mother who had to sell her body and a con man/swindler who served as a father figure and teacher. He shows little remorse for any of his more devious actions and appears sadistic at points when he takes pleasure in the misfortunes of his enemies. He is not above using any particular means to achieve his goals, such as threatening to murder Kaidou or using Kokorogi to blackmail a teacher.

History
Yuuichi Katagiri's past is somewhat a mystery currently, although it is known that Yuuichi has murdered three people and he has no idea who his real parents are. He was raised by his adopted mother Yuka Katagiri who had to sell herself to make money, which is a traumatic memory for Yuuichi. He also had a father figure in the form of a swindler named Taizen Shiba, who taught him various psychoanalytic techniques and mentalist tricks. Though he uses these to great effect throughout the series, he does not respect Taizen in his memories. He seemed to look up to him as a child, but he calls him a devil and scum at various points in the story. When trying to get Satone to back down from their game, he reveals that Taizen is one of the three people he's killed.
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