He was different, he was ill. People thought he was weird. Before knowing him, Cha Jinhee was indifferent. She was an ordinary girl who just wanted to live the ideal, drama-free years of high school without having to mind other people's business. While secretly facing his hurdles of living alone with an abusive man, Kim Wooshin chose Cha Jinhee to discover him, entering her life as the most annoying, egoistic, narcissistic, mischievous chairmate she'd ever had. Things began to change when she found a completely different person - Kim Wooseok, a soft-hearted bullied nerd who couldn't stand up for himself - living in the very same body, which led her to a deep dive and discovery of not just two, but three, four, and more shattered personalities hidden inside him. How would things turn out if her heart also changed for the mentally ill boy? Follow Jinhee and Wooseok's journey as she helped him open up to learn about trust, friendship, rivalry - and even love.