Rinka Okino is Kazuki Okino's younger sister, possessing brown hair and brown eyes and typically appearing as a teenager. Her personality involves teasing others and exhibiting a stubborn determination to achieve her goals, employing her feminine charms when necessary. Outwardly cheerful, she secretly harbors romantic feelings for Kazuki, fueling jealousy over his close relationship with their childhood friend, Otome Sakuragi. This jealousy drives her actions. She orchestrates a scheme involving DVDs depicting Otome exploited by older men, sending them to Kazuki to shatter his mental state and his relationship with Otome. Later, she arranges to be seen entering a public bathroom with an older man, further distressing Kazuki. After Kazuki discovers her role, Rinka confronts him, revealing her manipulation of events. She admits to past exploitation under similar circumstances, claiming her actions stem from Kazuki's desire to marry Otome instead of her. During this confrontation, she expresses her wish to bear Kazuki's child. The narrative concludes ambiguously: Kazuki experiences Rinka's involvement as part of a nightmare. Upon waking, he finds himself in an alternate reality married to Otome with a daughter. However, the discovery of one of Rinka's DVDs in this new reality leaves the nature of her existence and influence unresolved.