Rin Eba is the younger stepsister of Yuzuki Eba and biological younger sister of Itsuki. Initially presented as a petite girl sporting short red or pink hair just above her shoulders, she often wore a bored expression. Her appearance undergoes a dramatic transformation as the story unfolds: she gains roughly half a foot in height, her hair grows longer, and her physique develops pronounced curves, hips, and breasts. These changes are so significant that former acquaintances frequently fail to recognize her later. Her personality is mischievous and troublesome. Early on, Rin displays a strong attachment to her brother Itsuki, bordering on a brother complex, and expresses irritation toward Yuzuki, whom she accuses of feigning kindness for attention. She deliberately lies to upset Yuzuki, revealing manipulative tendencies. While her relationship with Yuzuki improves over time, she retains her provocative nature, which evolves toward a more overtly flirtatious and nearly promiscuous demeanor. Despite her penchant for mischief, she plays instrumental roles in forcing other characters to confront their feelings, often through questionable methods. A notable instance occurs when she becomes depressed upon learning Haruto and Yuzuki became sexually intimate, though she later rationalizes this doesn't guarantee their permanent union. Rin first appears arriving at the dormitory of Haruto Kirishima's sister in Tokyo, where Yuzuki is staying. She reveals she instigated Yuzuki's move to Hiroshima and initially refuses to accept Yuzuki as a sister, fearing displacement in Itsuki's affections. Her words later prompt Haruto to return to Tokyo to investigate Yuzuki's reluctance to stay. After Haruto confronts Itsuki about Rin's motivations and strikes him, Rin vows to target Haruto next. During summer break in Hiroshima, Rin stays with Haruto and Yuzuki. Haruto assigns Takashi Yura to show her around, leading to Takashi's infatuation. Discovering Haruto's interest in Nanami Kanzaki, Rin deliberately informs Nanami that Haruto went to Tokyo with Yuzuki instead of shopping, significantly contributing to Nanami rejecting Haruto at a summer festival. Before returning to Tokyo, Rin spends time with Haruto at the Hiroshima bus station, where both acknowledge previous misjudgments. Later, Rin tips off Nanami about Yuzuki's supposed new boyfriend, prompting Haruto's move to Tokyo. When Haruto visits Yuzuki's house, Rin claims Yuzuki is absent despite Haruto glimpsing her through a window. Years later, Rin reappears with a mature appearance, working at Haruto's convenience store. She announces her intent to attend Seijou University and manipulates Haruto into a campus tour. During this, she grabs his arm and falsely declares them a couple, causing embarrassment. She later challenges Haruto's relationship with girlfriend Asuka Mishima, claiming she could offer him a better time, and engineers a situation forcing Haruto and Yuzuki to visit Disneyland while she observes from afar. In a subsequent Hiroshima visit, Rin directs mischief toward Takashi and Kiyomi Asakura, provoking Kiyomi's jealousy by flirting with Takashi. After Asuka confronts Haruto about his lingering connection to Yuzuki, Rin questions Haruto about his conflicted emotions. She eventually acknowledges her own romantic feelings for Haruto but denies them outwardly, asserting she merely feels left out after learning of his intimacy with Yuzuki. Despite this denial, she privately resolves not to relinquish her pursuit. Physically, Rin's height increases from 148 cm to 162 cm, her weight stabilizes at 46 kg, and her blood type is AB. Her three-size measurements develop to B86/W56/H87 as she matures.