Jun Kirishima thrives as a popular, sociable student at Seikoku Academy and a key member of its gymnastics club. Her cheerful, outgoing nature fosters easy connections, earning widespread admiration among peers. This public persona masks a hidden life: she secretly leads an anti-bullying group called Kings and Jokers (KJ). KJ originated from supporters during her brief independent idol career, with the insignia derived from her initials, though misinterpreted by others as a gang symbol. This dual identity reflects her drive to protect others while maintaining normalcy.

Her strong intuition drives her to investigate anomalies, like the mysterious circumstances surrounding "Akagi." Beyond academics, Jun engages in street battles against local gangs, displaying physical prowess comparable to fellow pilots Yamato Ichidaiji and Ryugo Hijikata. This aptitude leads to her recruitment by Genta Ibushi of Oblivion Bay to pilot the twin-seater Megaton-class artillery mech, Rogue Maximus, designed for heavy firepower. As primary pilot, she must synchronize with co-pilot Momoka Saotome, despite their longstanding personal rivalry rooted in extracurricular clashes.

During a critical battle coinciding with Shelter Ixia's takeoff, Maximus sustains severe damage. Jun ejects Momoka to safety but chooses to remain aboard, continuing to fight despite imminent danger. This decision results in mortal injuries. Reiji Amemiya later revives her using his latent Psycho-Rise healing abilities. This near-death experience and resurrection mark a pivotal character development. Following revival, she resumes piloting duties alongside Momoka in the repaired and upgraded Maximus Blaze.

Complexity emerges in her interactions with Reiji after her revival, particularly as his protective instincts extend toward her alongside his known concern for cats. Her role within the pilot team solidifies through continued cooperation in battles against the Draktors.