Imura and Riki Oh both entered the prison together. In their first living quarters they were friends.Though they weren't especially close, Riki Oh revealed more of himself to him. Imura also always helped other prisoners when they needed help or were sick. He was once assaulting a traitor, but got stopped by Narumi. Saying something bad to Narumi enraged him, and he got a saw into his head.  Imura was later hanged on a cross as a bait for Riki Oh.   ~!However, Riki Oh arrives too late and Imura dies.!~

In the late 1990s, society is descending into ecological collapse and totalitarianism. Saiga Rikioh, 21, finds himself in jail. 
Set in the near future, at the privately-owned Tokyo State Prison. Like the chilling wind of the end of a century, a mysterious man with a six-pointed star on his fist entered the pen. 
Saiga Riki-Oh--serving a term of three years, due to assault, his first offense. Riki-Oh openly antagonizes The Four Emperors, four powerful prisoners that control the prison and keep the rest of the inmates in line.

A Retelling of the prison arc of the manga RIKI-OH! 
The story follows Saiga Riki-Oh, a young man blessed with inhuman strength. After taking revenge against a yakuza boss who was responsible for the death of his girlfriend, he ends up in a maximum security prison owned by a private organization. 
The prison is divided into four blocks, each run by a member of prisoners known as the Gang of Four. The first member is a tattooed knife wielder known as Hai that runs his block in a mafia style family system. The second member is a giant man (known as Tarzan in the live action) with incredible strength. The third member is a effeminate fighter named Huang Chaun that is growing Opium in the prison. The final member is a small man that use sewing needles as his weapons.

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Son of voice actor [Chikao Ootsuka](https://anilist.co/staff/95974/). In 2005, he married fellow voice actress [Youko Soumi](https://anilist.co/staff/95912/), but they divorced in 2009.

__Non-Anime Roles:__

- Heismay Noctule - Metaphor: ReFantazio (VG)
- Koichi Adachi - Yakuza: Like a Dragon (VG)