A kogal who took the country by storm with her extravagant tastes. Junko wanted to be a model ever since she was a child, but is also eager to try new things. She used to be homeless.
END GAME SPOILERS
It is discovered that the girl who introduced herself as Junko wasn't really Junko at all, but actually Mukuro Ikusaba, a Super Highschool Level Soldier (aka Junko's sister). She was the "victim" of the fifth murder, her body having been used to create a fake crime scene. The real Junko, her younger twin sister who she switched places with, was the mastermind behind Monobear. She appears in the flesh at the end of the game, once her attempt to mask Mukuro's murder becomes uncovered.
The real Junko's personality and mannerisms tend to be very erratic and unstable, switching through several "personalities" at the drop of a hat, as she finds being the same all the time boring. She is obsessed with despair and finds it to be one of the most enjoyable emotions in the world. She is incredibly manipulative and cunning, having orchestrated the Worst, Most Despair-Inducing Incident in the History of Mankind.
Her talent as SHSL Fashion Girl is only superficial, derived from her true talent, SHSL Analyst. This allowed her to be able to predict the outcome of events, making her bored with the world, which is why she took interest in despair as it is unpredictable and exciting for her at a very young age. She used the fake identity Ryoko Otonashi, the protagonist of DR/Zero, with her title as SHSL Analyst. She also used her talent to manipulate people with the data she acquired from them. After her death, the remaining students she brainwashed that contributed to the Worst, Most Despair-Inducing Incident in the History of Mankind came to be known as the Remnants of Despair.
