Outwardly, Nezumi is a rude, sarcastic, and irritable individual, especially when he feels as if he's being questioned. Every time Shion asks Nezumi about himself, Nezumi shortly tells him to stop being nosy. When speaking with others, he often takes on a condescending or mocking tone. Nezumi has a cruel streak when it comes to getting what he wants, such is demonstrated when he tortures the No. 6 official, Fura. However, no matter how much Nezumi denies it, he is capable of thoughtful gestures. At some point, Nezumi gifted Shion's sweater to the young girl, Karan.
Nezumi also has a tendency to to be dramatic and theatrical, due to his love for classic literature. His room is filled with books that range from Shakespeare to Ecology and Scientific Journals. For someone who has no formal education, Nezumi has a vast amount of knowledge. However, he is unorganized – a fact that is noted by Shion and proven by how messy his room is. In addition to being booksmart, Nezumi's instincts and survival skills are as sharp as his knife.
At the beginning of the series, Nezumi is a very cold individual who keeps himself distanced from others. He stands firm to the belief that you should live only for yourself, that memories and relationships are like shackles that ultimately lead to your downfall. As the series progresses, this resolve crumbles. He becomes protective and fond of Shion, and there are a number of times he puts Shion before himself. [Source: wikia]