Natsumi Kuzuryu is a character in Danganronpa 3: The End of Hope’s Peak High, and she has no Ultimate title as she is a part of the Reserve Course. Natsumi exhibited extreme egotism and smugness upon introducing herself to Hajime and the rest of the Reserve Course students in his class. Natsumi was described by many as a mean and egotistical girl who’d plant hatred towards someone she dislikes or envies. Natsumi is also said by her parents to be much more violent than her brother and more worthy of being the Yakuza heiress than her brother. As described by Fuyuhiko, Natsumi was used to making a fool out of him every day and always pissed him off, but Fuyuhiko always considered her as his cute sister, and the two most likely had as much of a normal sibling relationship and cared deeply about each other. However, underneath her self-centered and tough exterior, Natsumi was an insecure girl who did not want to be left behind by her brother and was willing to talk with people who did not treat her harshly, such as opening up to Hajime about her inner struggles despite the two not knowing each other too well. While she could threaten people, it implied she wasn't serious about it and, as a yakuza, was used to talking that way. After Sato became protective of Mahiru and started pestering Natsumi about her intentions, she already appeared tired of the topic and wanted to be left alone.

Voices for Reference (ENG): https://www.youtube.com/watch?v=h1m-5CUFcjU 

More info on her role in the THH Remnant AU: https://www.tumblr.com/spittyfishy/tagged/natsumi%20kuzuryu