Rinka Kunitachi is a first-year student at Miryuin Private Academy and the diligent vice-president of the student council. Born into nobility and raised with strict etiquette, she often appears distant and formal, rarely seen outside her school uniform—accessorized with a blue ribbon and a left-side braid. This upbringing fosters a serious, no-nonsense attitude, leading her to establish a Moral Committee to combat declining student morals and causing others to perceive her as haughty or uptight. A competitive nature underscores her reserved exterior.

Beneath this formality, Rinka possesses a loyal and friendly core, occasionally revealing a less mature, childish side. Her loyalty is demonstrated when she fabricates a phone call to protect Shougo Mikadono from a scheme by School Director Genda. Bound by an arranged engagement to Genda's son, which she resists due to her belief in marrying for love, Rinka was tasked by Genda with uncovering the identity of Shougo's illegitimate half-sister to gain leverage over the Mikadono Group. In response, she orchestrated a deceptive school broadcast announcement, falsely claiming to be Shougo's sister, intending to threaten Genda into halting his investigation.

After Shougo deduces her scheme, he proposes pretending to be her lover to void the engagement. This collaboration marks a turning point for Rinka; she shifts from viewing Shougo as a means to an end to genuinely pursuing him romantically. Her interactions with him soften her rigid demeanor, showcasing newfound trust and emotional vulnerability.

Her refined upbringing endowed exceptional skill in traditional activities like dancing, cooking, and marksmanship, though her sheltered life left her inexperienced in common leisure pursuits like visiting amusement parks. As vice-president, she frequently manages responsibilities neglected by the carefree president, Mana Tendou, reflecting her strong sense of duty.