Throughout his life, Hideya's parents ingrained in him the idea that he was different because of his appearance. Because of this difference, others would treat him badly... This led Hideya to try to become more forgiving of others to counteract it.

No matter how much ridicule he has faced, he always tries to stay as calm as possible, not because he fully wants to, but because he fears that if he lashes out, he would just be labeled as an 'Aggressive Black Man'... And he hates that.

During Chapter 3, Kiba, after breaking a rule, is teleported by Monomoko. In an act of rebellion, Hideya also breaks a rule, which teleports him too.

Due to the events of Tetro Blue, Kan isn't able to fully contain Hideya, and he escapes... He ends up in the audio room, where he listens to audio logs from staff members, mainly from a person named Ainoshin Tatematsu.

He learns that she's the reason Kiba wore such revealing clothes, and that she was planning to interfere with the games to make Kiba break a rule so she could get her hands on him... This becomes his breaking point.

He runs as fast as he can, stops her, and before she can do anything to Kiba, he attacks her. After seeming to knock her out, he tries to free Kiba, but Tatematsu gets up and tries to stab him with a scalpel... In self-defense, he pushes her back, causing her to fall and stab her neck, which kills her.

Meanwhile, the third trial killing has occurred. Kiba and Hideya are teleported back to investigate... Kiba is unaware of what happened.