Tokuzo Sugiyama is the warden of Kokubu Prison, a privately owned maximum-security penitentiary in a post-apocalyptic near future. He oversees a facility where the most violent inmates effectively govern the cell blocks under his tacit approval, using a hierarchy of prisoner bosses to maintain control. His background is largely undisclosed, but his position answers to a higher authority known as the Chairman.

Sugiyama is a sadistic, cunning, and ruthless individual who derives pleasure from the suffering of others. He views the prisoners as expendable tools and does not hesitate to sacrifice them to achieve his ends. His primary motivation is the preservation of his own power and standing; when the arrival of Riki-Oh threatens the established order, Sugiyama becomes obsessed with eliminating him, partly out of pride and partly because the Chairman warns that failure will cost him his post.

In the story, Sugiyama serves as the main antagonist of the prison arc. He systematically sets traps for Riki-Oh, ordering the North Wing boss Narumi to beat an innocent prisoner nearly to death to provoke a conflict, hoping that Narumi will kill Riki-Oh. When that plan fails and Narumi is killed, Sugiyama escalates by enlisting the other wing bosses and eventually confronting Riki-Oh directly in the climax alongside the Chairman and the South Wing boss Yomi.

Sugiyama’s key relationships are defined by authority and manipulation. He commands the prisoner bosses who rule the four wings, including Narumi and Yomi, and he is subordinate to the Chairman, who holds ultimate control over the prison. His interactions with Riki-Oh are adversarial, as he attempts to break the protagonist through orchestrated violence and psychological pressure.

Throughout the arc, Sugiyama’s character undergoes no redemption or change; he remains relentlessly cruel. His development is primarily a progression of failure as each scheme against Riki-Oh backfires, leading to a desperate final confrontation. He possesses no supernatural abilities or exceptional physical strength; his power comes entirely from his official authority, his manipulation of the prisoner hierarchy, and his willingness to commit any atrocity to maintain control. He is ultimately killed in the battle with Riki-Oh, marking the end of his reign over Kokubu Prison.