Niizuma is slightly naive, but can also be serious and calculating when he wants to. Eiji tends to act conceited because he is hailed as a genius; however, after working on Crow for quite a long time, he grew more humble, even claiming to not be "good enough of a Mangaka to be judging other people's work" when asked by his editor to judge for Jump's monthly award. (He judges anyway, but is not very helpful, only expressing his interest in Ashirogi and Ryu Shizuka). Niizuma shows great respect for his fellow authors, calling them sensei regardless of age. He loves manga, considering his job fun and reading every comic in Jump. He despises sleeping, but does so when needed. However, with how long he can stay awake, he will be out for a long time. His earliest assistant, Nakai, said Niizuma usually slept for 20 hours.

This character requires a lot of emotion and yelling, please keep that in mind. Example video (https://www.youtube.com/watch?v=gcRfcWtOsZ8)