u is described as an oddball, having an overly confident, loud personality and a frighteningly sharp tongue. She considers herself a beautiful genius, and every time she opens her mouth she spews a parade of reckless vulgar remarks and insults, strongly putting pressure on others and looking down on them. In the original Japanese, she even uses the Japanese word "ore-sama" to refer herself, which is considered very arrogant and more traditionally masculine. She also tends to give other characters insulting nicknames.

However, Miu's arrogant personality seems to be only a mask which can drop fairly easily. This often happens when her festival of coarse language and dirty jokes actually get replied or ignored. Then, her personality quickly changes into a timid weakling, who is terrified of other people being angry with her. Because of this, she has the charm similar to an innocent child.

Created to be the "naughtiest character in the series' history", Miu appears very perverted and openly says bizarre, obscene things during her arrogant mood, meaning almost constantly. She often claims that she just says them to lighten up the mood, but they are very much disliked by the other students. Despite often trying to act dominant and appear sadistic, Miu is also masochistic and into BDSM, and acts very different during her weak-willed moments. Despite her usual arrogant behavior, she seems very uncomfortable if other people actually act very submissive towards her, like when Kaede and Shuichi begged for her help and she begun to sweat nervously and agreed just to make them stop (though she later claimed that the situation turned her on).