Denji is both brash and naïve 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.