As a young fashionista, Junko is described as simply "not fake", charismatic and eager to try new things. During her first appearances, she comes across slightly air-headed and hot-tempered. In the official artbook, she is described as a person who "drips with dissatisfaction the moment she opens her mouth" and tends to be in trouble with her classmates. She is also mentioned to be a bit too talkative with an overly carefree attitude. However, Junko's real personality, revealed at the conclusion of the Killing School Life, is notably different: very apathetic and easily bored to an unhealthy and abnormal degree. Because of this, her behavior and mannerisms tended to be extremely erratic and unstable by her own autonomous design; keeping up one "appearance" for too long bores her, which causes her to often switch between different personas. However, she is capable of maintaining one persona for extended periods of time when necessary, such as when she was overseeing the students through Monokuma. Junko's "moods" included (but were not limited to) her Monokuma persona, sickening cuteness, severe depression, clinical sophistication, boisterous vulgarity, eerie stoicism, and haughty superiority. She switched between "moods" regularly, often imitating other students' expressions, which made for a highly unsettling conversation with the survivors. While entering the Hope's Peak Academy as one of Class 78's students, she often talked as if narrating a story, writing down her thoughts in a notebook.

https://www.youtube.com/watch?v=1uJ1Jg5Pj4U&t=18s