Yuuya is a mysterious character at first, indicating nothing of his true personality. He initially appears to be a protective and strong ally, as well as sophisticated and classy with his Japanese pronouns, language, and manners, though occasionally coming across as somewhat blunt and apathetic. 

Underneath this façade, however, Yuuya is a sociopath in the truest sense, withholding no understanding or comprehension of morality, affection, social interaction, or the value of life. After coming to Heavenly Host, he at first attempted to work with his "friends" to escape. However, after the deaths of several classmates, he came to the conclusion that it didn't matter in the slightest how a person died, since they were going to anyway, giving Yuuya the justification he needed to murder those around him.