Enter the gripping narrative of RIKI-OH as it delves into the intense prison arc. Saiga Riki-Oh, gifted with extraordinary strength, seeks vengeance against a yakuza boss for his girlfriend's demise. His quest lands him in a high-security prison controlled by a private entity. Inside, the prison is segmented into four blocks overseen by the formidable Gang of Four. Hai, a tattooed blade expert, rules his domain akin to a mafia don with a tight-knit family structure. Tarzan, a colossal powerhouse, commands another block with his unmatched might. Huang Chaun, a delicate yet fierce combatant, tends to illegal Opium cultivation within the confines. The quartet is completed by a diminutive figure utilizing sewing needles as deadly instruments, adding a layer of intrigue and danger to Riki-Oh's harrowing ordeal.