Akari enters high school hoping to remain unnoticed and has little expectation of becoming the center of anyone’s attention. On the first day she finds a love letter in her locker that turns out to be a fully prepared marriage proposal from Luna Kiyosumi, the most visible and admired girl at school. Akari’s quiet plan for adolescence collapses immediately as she tries to understand why Luna chose her and how to respond to a relationship moving much faster than she ever imagined.