Denji is both brash and naive as a result of being unable to have a formal education and socialize due to living in severe poverty. His personality comes off as rude and harsh in an almost childish way. However, he has a good sense of empathy towards other people, willing to save those in danger as much as he could, showing he is a kind hearted person despite his shortcomings. While Denji doesn't necessarily possess the highest intelligence, he is capable of clever ideas to take down devils, such as lighting himself on fire and using the light emitted to weaken Santa Claus enough to kill her.