Minju is top of her class, quiet, focused, and allergic to school drama. Noh Yunah is everything she can't stand: popular, loud, reckless... and rumoured to leave a different girl heartbroken every week. When Minju is forced to be Yunah's lab partner, she expects the worst. But behind Yunah's smirk and reputation is someone unexpectedly thoughtful and deeply insecure. The more time they spend together, the more Minju starts to question what she thought she knew about Yunah. And Yunah? She's already fallen. She just doesn't believe someone like Minju could ever feel the same.

Every Wednesday, Noh Yunah finds a letter waiting in her locker that is anonymous, thoughtful, and written with a familiarity that lingers. She never asks who it's from. Park Minju lives quietly on the edges of the same school, keeping her world small and controlled. Writing is the only place where she allows herself to be honest. As senior year unfolds, routines begin to shift, and what has remained unsaid for years starts to press gently but persistently toward the surface.