She is the founder of Ultimate Despair (超高校級の「絶望」chō kōkō kyū no “zetsubō”), known as the True Ultimate Despair.
Junko has the title Ultimate Fashionista (超高校級の「ギャル」chō kōkō kyū no “gyaru”), which allowed her to be scouted to attend Hope's Peak Academy. However, multiple installments in the series have revealed that this is only a superficial talent, derived from her "true", inherent talent of being the Ultimate Analyst (超高校級の「分析力」chō kōkō kyū no “bunsekiryoku”), which borders on superhuman.
In Danganronpa 3: The End of Hope's Peak Academy Junko appeared as the person responsible for the corruption of the Remnants of Despair. Sometimes during Side: Despair, Junko created her alternate identity known as Ryoko Otonashi in Danganronpa/Zero. During those events, she murders her beloved childhood friend Yasuke Matsuda in a fit of despair.
During the Killing School Life, Junko executed her older sister, Mukuro, who was masquerading as her, using Monokuma.
Junko executed herself along with Monokuma after her despair was defeated by the survivors' hope and was voted guilty in the last trial of Danganronpa: Trigger Happy Havoc.
Junko returns in Danganronpa 2: Goodbye Despair as an Artificial Intelligence and a virus. AI Junko also appears in Danganronpa Another Episode: Ultra Despair Girls, in the form of Shirokuma and Kurokuma.
At the end of the story, all of Junko's despair is defeated as the Remnants of Despair restored back and converted from despair and Makoto with help from the Future Foundation rebuild the Hope's Peak Academy. As she is dead, Junko can't intervene with the story ever again and only could watch the event folds in the afterlife. For the same motive, she don't care about the world now and is already satisfied with all despair that she accomplish and the fact that the world without despair is despair itself.
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 art book, 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 overly carefree attitude. However, Junko's real personality that is revealed at the conclusion of the Mutual Killing incident of Class 78th is notably different. Her true personality appears to be very apathetic and easily bored, to the 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, and haughty superiority. She switched between "moods" regularly, often imitating other students' expressions, which made for a highly unsettling conversation to the survivors. While entering the Hope's Peak Academy as one of Class 78th students, she often talked in her narration-style and writes it in a notebook.
Above all, Junko was deeply obsessed with despair, having found despair to be the most (and possibly the only) enjoyable emotion for her, whether it be the inflicting of despair unto others, or suffering from despair wholeheartedly. This made her extremely dangerous, as she wished to make the whole world feel absolute despair. However, this also often proved to be her biggest weakness, as she gave her opponents a "fair" chance to defeat her in order to make their despair all the greater if they fail, and happily welcomed her own despair if her plans fail. Both Junko herself and the game's creators have confirmed that she truly has no reason to do things she does other than despair itself, which makes her all the more dangerous and unable to reason with. Danganronpa/Zero proves that she wasn't born with the hunger for despair, but it developed at quite a young age due to an unknown reason.
In Danganronpa/Zero, it's also revealed that she possesses near supernatural analytical skills, which is her true talent. In Danganronpa 3, it's implied that similar to Izuru Kamukura, this talent is the reason why she is easily bored with the world and seeks out unpredictable despair to free herself from the said boredom.
As a mastermind and leader of Ultimate Despair, Junko was shown to be highly intelligent, cunning, somewhat impulsive, and extremely manipulative, violent and cruel without remorse. She manipulated people into falling madly in love with her and used their weaknesses, their despair, against them. Things like hope, peace, and happiness disgusted her, but she sometimes gave hope to others, only to turn it into despair later. She often manipulated people into doing bad things instead of directly doing them herself, and then had a habit of blaming these manipulated people and claiming it wasn't her fault, as a part of proving her point that despair exists in everyone and that hope will naturally lose to that despair.
While very abusive and cruel even towards her loved ones, it's implied that she felt some care for them, in her own messed-up way. It is interesting to note that the two people who Junko loved the most (Mukuro and Yasuke) are the only people shown in canon to be killed directly by her: Mukuro through the Spears of Gungnir and Yasuke through stabbing, whereas Jin Kirigiri was killed indirectly through an execution. This is likely because killing those she holds most dear would cause her great despair and to Junko, the greater the despair, the better.
- Junko was resurrected by Lord Zedd and Rita Repulsa, and with a little magic, she no longer had to switch between "moods" (except for her normal, intellectual, drama, royal, rocker, rage and Monokuma persona) ever again. Plus, she became Montana Max's beloved girlfriend.
- Junko hates Elmyra with a passion, so she always scares her away by using her Monokuma disguise.
- Thanks to her resurrection, Junko is now both Ultimate Fashionista and Ultimate Despair.
- Just like Azula, she, too, is given the power to become Wicked Lady, only that it was thanks to Lord Zedd and Rita Repulsa.