Kokushibo is reserved, silent, and aloof, maintaining an aura of unnerving tranquility and mystery that compliments his position as Upper Rank One. He rarely speaks; when he does, he talks in a slow and emphatic manner. He possesses a complex relationship with his human past. It is revealed that as a human, Kokushibo harbored an immense sense of envy towards his younger twin brother, for his natural talent and incredible abilities.