Kirara Hoshino serves as a core combatant in the HxEros team, battling invasive alien entities known as Kiseichū. Her personality underwent a profound shift rooted in a traumatic childhood encounter with these aliens. As a child, she shared a warm and open friendship with Retto Enjō. This closeness shattered after a Kiseichū attack specifically targeted her H-energy—a vital life force intrinsically linked to human passion and sexuality. The violation instilled deep shame regarding her own libido and sexuality, triggering a drastic behavioral change. She developed a severe aversion to males, actively distancing herself from Retto and meticulously avoiding physical contact or objects handled by boys. Despite this self-imposed estrangement, underlying feelings for Retto persisted, hinting at unresolved emotional connections beneath her cold exterior.

Operating within the HxEros team alongside Retto and three other female members, Kirara channels H-energy into potent combat abilities to counter Kiseichū threats. The series positions her as a central figure in the team's dynamics, heavily influenced by her complex history with Retto. While a prudish demeanor initially defines her interactions, the narrative progressively uncovers the origins of her behavior, revealing it as a trauma-induced response of embarrassment and shame rather than an innate trait. Her journey involves navigating this self-imposed emotional isolation while fulfilling missions demanding teamwork and intimate energy collection.

Kirara's character development focuses on reconciling her past trauma with present relationships. Gradually, she confronts the psychological barriers erected after the alien attack. This confrontation culminates in Retto confessing his feelings, an act that catalyzes her emotional reopening. By the series' conclusion, they reconcile and establish a romantic relationship, marking her recovery from the childhood incident and her acceptance of both her own sexuality and her enduring connection with Retto.