Shiro Kirishima and Akane Hayasaka are high school classmates who share a secret. In public, they maintain a polite distance, but in private, they act as lovers. Their relationship is not born from mutual affection but from mutual convenience. Shiro is in love with the student council president, Hikari Tachibana, but she already has a boyfriend. Akane, an honor student popular with her peers, harbors feelings for someone she cannot be with: Yanagi, an older man who was Shiro’s senior in elementary school. Unable to pursue their true first choices, they agree to be each other’s second best. Their arrangement is built on a simple promise: they will provide each other with the comfort and intimacy they crave, but the moment either of them has their feelings reciprocated by their true crush, the relationship will end.

The story follows Shiro and Akane as they navigate this fragile agreement, which they initially view as temporary. Despite telling themselves their bond is merely a placeholder, the more time they spend together in secret, the more complicated their emotions become. They walk home together, share secrets, and grow physically intimate, blurring the lines between a convenient arrangement and a genuine connection. The conflict deepens as both continue to pursue their respective first choices. Shiro bonds with Hikari over a shared love of literature, making her the subject of his lingering affection, even as she remains engaged to her wealthy boyfriend. Meanwhile, Akane’s admiration for Yanagi persists, creating a constant tension between her past feelings and her growing attachment to Shiro.

As the series progresses through its eight volumes, the initial premise evolves into a messy and dangerous love triangle, or more accurately, a love square. The narrative explores the psychological consequences of their arrangement as each character is forced to confront the possibility that their first choice may not be what they truly want. The story moves beyond their high school setting when Shiro goes to university in Kyoto, where new friends like Akira Tono and Shiori Miyamae enter the picture. However, the central turmoil remains with Akane and Shiro, as their act becomes something real and unexpected. Their promise to end things the moment true love calls begins to feel impossible to keep, leading to an irreparable, complicated entanglement where lust, convenience, and genuine affection become indistinguishable.