Natsumi had demonstrated extreme egotism and smugness upon her introduction to the rest of the Reserve Course students. In Twilight Syndrome Murder Case and according to Girl E, Natsumi was described as a mean and egotistical girl who would plant hatred towards someone she dislikes or envy. Natsumi is also said by her parents to be much more violent than her brother and more worthy of being the Yakuza heiress.

As described by Fuyuhiko, she was used to making a fool out of him everyday and always pissed him off, but Fuyuhiko always considered her as his cute sister. When she cooked fried noodles during the temple festival, a huge line would form outside the temple. She also got an insane number of contracts from hand towel companies. She is self-centered, selfish, and extremely arrogant. However, she had a subtle way of making people do what she wanted.

(Source: Danganronpa Wikia)