|Killed by||Wretched Egg|
|Occupation||Middle School Student|
|Manga debut||Chapter 1|
|Anime debut||Episode 1|
Yamakatsu had been friends with Ganta and Mimi for a long time. In chapter 4, they are seen getting ice cream at an ice cream stand called "Hayashinaga Ice Cream" after school. Yamakatsu and Ganta were broke and had to ask Mimi for cash for the ice cream. A year before the start of the series, Yamakatsu and his other classmates went to a waterpark for a school trip.
Yamakatsu was a fairly kind individual who wasn't above teasing his friends. He appeared to have in interest in soccer. According to Ganta, Yamakatsu had a porn stash. 
Yamakatsu had dark skin, short, spiky brown hair and brown eyes. He was seen wearing his school's uniform which consisted of a plain white shirt with the school's logo stitched onto the breast pocket and black pants.
Yamakatsu is first seen in a classroom at Nagano Middle School teasing his friend Ganta Igarashi. Whilst discussing their upcoming school trip to Deadman Wonderland, Ganta's past and the Great Tokyo Earthquake, the students see a crimson man floating outside their classroom window. The crimson man smashes through the walls of the classroom and slaughters every student inside excluding Ganta.
- Yamakatsu's last name, Katsuya, is only ever mentioned by Mimi's father in the anime.