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. Despite appearances, Mishima is an incredibly kind, caring and encouraging person. After his A.I. self learned about how much suffering Nao was going through after his death, he could only blame himself for it. He deeply regrets not being able to live longer, because he truly just wanted to protect Nao. He also regrets not being able to live on to see Nao continue to grow, as well as his other students.

He's shown to not only be caring towards Nao though, but he also shows great concern for Kanna and even helps to spur her onward towards hope, albeit by lying about the circumstances of the first trial.

Not much is known about Mishima's life, though his A.I. self mentions only two major points in his life; these being the day he became a teacher and Nao Egokoro's graduation. Even after Nao's graduation, she still visits his atelier to learn more about art from him. He greatly cares for Nao and their bond is incredibly strong.