Being a little odd, Mishima often puffs mad scientist laughs after sentences, and his emotions often conflict with his appearance. Mishima seems to enjoy acting strange to amuse others, behaving cryptic and overly analytical of everyone's actions. His unusual social quirks aside, Mishima makes it clear he has no ill intentions and frequently reminds others to be safe and cautious. 

Mishima does not have as big a role as the others participating in the death game, because he dies in the first part. Though he appears as an AI in chapter 2, so I would like if you stuck around through the whole thing. I imagine his voice to be like the typical mad scientist and have a medium pitch.