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.  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, absolute simple for Mr. Makima, the control devil.