Appearance and Personality
Hiseki carries an intense desire for revenge against the Yukimura Zaibatsu, stemming from traumatic events in his childhood. Despite this he seemed to have a sense of humor, when he decides to play a game of riddles with Tokio Morishima to reveal his story to him in his final days.
Hiseki spent his childhood in the rural industrial town of Mikumo 77. He was childhood friends with Sumio Kodai, Fuyuki, and Riru Yukimura. The river near the town became gradually polluted by chemicals as a result of the activities of the Yukimura Zaibatsu. Due to the narcotic effects of the run-off, the protesting residents became gradually more violent. These riots became colloquially known as The Parade. During the Parade riots, Riru, abandoned by her parents as a "sacrifice", is targeted by townspeople who believe she is a witch. On August 2nd, 1979, she is taken from her home, raped, and killed by the crowd of rioters. For their efforts to rescue Riru, Hiseki and his friends are attacked and disabled; Hiseki's eyes were gouged out and sewn shut, rendering him blind. After this, Hiseki and his friends formed the Mikumo Boys, and began a 20-year plan to get revenge.
The Mikumo Boys met up repeatedly during this period to plan their operation. This is hinted at in the supplemental manga Pre-Lunatics, where Sumio mentions having a date with "two monkeys" during the events of case#0:lunatics. Hiseki also assisted Sumio by creating special communication software that converted speech into Braille, for him to blend in and appear not to be deaf. Hiseki used similar equipment to operate computers. On July 7th, 1999, Hiseki received an email from Tokio Morishima, who believed he was The Bat. Hiseki decided to put on a "parade" for Tokio by sending him a series of riddles relating to his background and the events at Mikumo 77, which he began invesigating alongside Erika Yukawa.
On July 11th, the plan went into action with the kidnapping of Chairman Yukimura and the destruction of the Yukimura Estate, thanks to a bomb planted by Hiseki. He then planted another bomb at Snow Tower, to be detonated by the Chairman later. He also arranged a delayed email to be sent to Tokio after his death, revealing his true identity. After this, he killed himself by hanging. On July 19th, his body was discovered at his apartment by the Heinous Crimes Unit. Later he and the other Mikumo Boys' plan was fulfilled by the complete destruction of the Yukimura Zaibatsu's board of directors, and finally the town of Mikumo 77 on the 20th anniversary of Riru's death.
- The Mikumo Boys represent the Japanese maxim of the "three wise monkeys", origin of the proverb "see no evil, speak no evil, hear no evil". The monkey who covers his eyes is known as Mizaru, a name shared with a character from killer7.