Kim Jongin, who prefers to be called Kai, is a lost mind. What is a lost mind? And how is he 'lost'? A lost mind is a mind without a person. A person always has a mind, right? Well, Kai used to be someone's mind. That is until the person had disappeared, leaving him stranded in Seoul where he no longer has a person. So from then on, he became a lost mind. Cluelessly roaming Seoul, Kai is having fun but is still looking for his new person. So far, it's been unsuccessful. 

Park Junghee is quite popular at school. Being apart of leadership where they schedule and plan dances and all that matter, and being apart of SM High's popular dance group is what makes her well known. Beautiful, friendly, weird, and a ball of sunshine, Junghee gets along with mostly everyone at her school. Being both dependent and independent at the same time, she doesn't let anybody be her mind where they make decisions for her. 

A lost mind and a girl who doesn't let anyone be her mind, I'm pretty sure you know how their lives are going to intertwine together.