Haruna Kasuga serves diligently on her high school’s disciplinary committee, her earnest dedication and sense of responsibility countered by a gentle-hearted nature that lands her in humorous predicaments, especially when peers like Miiko and Kurumi drag her into mischief. Though stern in enforcing rules, her genuine kindness shines through, making her both respected and approachable.

An audio equipment enthusiast influenced by her father, she quietly resists diving into DJ culture, a contradiction that underscores the tension between her disciplined facade and hidden passions. Her striking maroon hair and gold eyes are often hidden behind contact lenses during school hours, though she switches to glasses at home due to poor eyesight. Towering over her peers, she frequents the tea ceremony club, regularly extending invitations to classmates, fostering camaraderie through shared tea gatherings.

Complex relationships deepen her narrative. She holds deep admiration for Aoi, addressing her with the reverent "-sama" and stumbling through interactions, even second-guessing a simple gratitude message. With Miyu, interactions brim with unspoken affection—Haruna’s jealousy flares when others command Miyu’s attention, yet she braves ghostly encounters to protect her. A pivotal moment unfolds during the "White Corsage of Dearest Love" event, where a daydream of gifting Miyu a corsage spirals into flustered panic. Later, Miyu presents her with a white marguerite—a token of secret love—sparking Haruna’s conflicted introspection.

Moments of vulnerability pierce her composure: a nosebleed erupting when Miyu voices affection for their group, or goldfish christened with blended versions of their names, hinting at her emotional thaw. Subtle quirks round her persona, like recognizing shoujo manga tropes or quietly enjoying *The Quintessential Quintuplets* after confiscating a copy—a guilty pleasure bridging her strict role and private self.