Adachi is voiced by Johnny Yong Bosch in the English version.

His true nature is that of a sadistic misanthrope who manipulates others for his own amusement, acting as if everything was a game and doesn't seem to care about the consequence of his actions. He believes that there was nothing great about the real world, calling it "boring," "shitty," "dull" and "annoying as hell" to him. He views his reasons for what he's doing as justifiable, saying that he wants to save and prevent humanity from the pain, suffering, boredom and despair of life.

Later, in Persona 4 Arena Ultimax, he retains his habit of taunting the cast, but also retains his cheerful, nonchalant attitude. The actions of the Investigation Team appear to have made an impact on him as well; he is very adamant in trying to atone for his past crimes and shows an immense amount of selflessness by attempting to destroy the Persona Fragments that Sho had collected and assisting Yu in defeating Hi-no-Kagutsuchi. In addition, although Adachi won't admit it out loud, he genuinely values his friendship with Dojima; smiling when Dojima came to visit him in prison and almost losing his temper when the middle-aged detective began insulting him.