At the time of his death, Mikoshiba wore a dark blue suit over a white buttoned-up dress shirt with a striped purple tie.
During his time as a student, Mikoshiba was a model student who had bullied Toshiro Ehara, leading to him committing suicide in 2018. Because the school did not want to tarnish its reputation by having one of its top students be revealed as a bully, it hid any evidence of Mikoshiba's misdeeds, allowing him to graduate unimpeded.
Eventually, he returned to Seiryo High for his alma mater and became a student teacher under the supervision of his former teacher Yoko Sawa. He would put students in the basketball club through rigorous exercise after the coach departed, and his method of punishing the entire club if one lagged behind led to Mami Koda being bullied, as her physical performance was inferior to her peers', and Mikoshiba himself also frequently berated her.
Lost Judgment: 2021
Mikoshiba is abducted by Jin Kuwana's former students and taken to an abandoned building, where he is tortured by his victim's father Akihiro Ehara. Though Mikoshiba pleads to be released and vows to atone for Toshiro's death, Ehara slits his throat and the murder is recorded on camera. His rotting corpse is discovered two months later, right before Ehara's sexual battery trial. Ehara's alibi for not killing Mikoshiba is the fabricated evidence of him committing sexual battery in the timeframe of Mikoshiba's death; a key part of a plan to tarnish the legal system's reputation.
- Although he is stated to be 21 on the news broadcast announcing his death, his in-game character profile states that he is 22.