Son was shown to be sadistic and cruel, as seen in the flashbacks of Mother's memories when he openly taunted and enjoyed the physical and verbal abuse she was being put through by Rui and Father, while addressing them formally as his parents, showing that he sadistically enjoyed playing the part of being in a "family". Similarly to Father, he was extremely loyal to Rui's cause and played his role as an elder brother in his family without question.

Like most demons, he hated humans; he was responsible for a great number of people transforming into spiders and even ruled over them, making them servants when their mental intellect eventually faded away with their transformation. His taunting and prideful nature was also evident when he continually prodded and mocked Zenitsu Agatsuma over his impending fate as a spider.

Son was also shown to be arrogant and brash, openly insulting his attacker's ability to do just one form and becoming enraged at the thought of dying at the hands of someone he thought so lowly of. In spite of his pride and confidence in himself, he became fearful upon seeing Zenitsu's true power being used and desperately tried to flee back into his house.