Reiji Kokonoe endured severe childhood trauma inflicted by an alcoholic father who subjected him and his mother to domestic violence. His mother's failure to intervene or escape nurtured deep resentment within him toward both parents. He felt no grief upon their deaths in a car accident. Relatives then relocated him to live with his cousin, Aki Kokonoe, who had a young daughter named Rin.

Initially withdrawn and mistrustful, Reiji gradually opened up through Aki's persistent kindness and the warmth of her household. He formed a close bond with Rin, experiencing genuine familial love for the first time. He later developed romantic feelings for Aki, and despite their cousin relationship and age difference, they married. Following Aki's death from lung cancer, Reiji became Rin's sole guardian. Honoring a promise to Aki to protect Rin at all costs, he manifested extreme overprotectiveness. He worked long hours to support her financially, struggling to balance this with caregiving duties.

Reiji harbored intense dislike for Rin's teacher, Daisuke Aoki, perceiving him as a rival for Rin's affection and fearing he might disrupt their relationship. This jealousy stemmed partly from Rin's overt crush on Aoki. Reiji's protective instincts darkened as he subtly groomed Rin to eventually become his wife, viewing her as Aki's replacement. His fixation fueled ongoing tension with Aoki, who grew suspicious of his motives.

Over time, Reiji's obsession waned, influenced by Aoki's role in helping him confront his trauma. He eventually overcame his romantic attachment to Aki's memory, shifting focus toward healthier relationships. In the narrative's conclusion, he developed authentic feelings for Mimi Usa, Rin's classmate. Recognizing shared vulnerabilities in Mimi, he chose to wait for her to reach adulthood before pursuing marriage and starting a family, symbolizing his emotional growth and departure from past destructive patterns.