Kion, haunted by his past, meets Ell, a girl who does not remember him from high school. Whenever they spend their summer in the same town, Kion tries to get his revenge and peace through her; but once confronted, they see each other as something different than what they thought. Kion works with his few close friends at the local diner, a place that Ell thought to be past her living standards. Once she visits it though, she sees a different side of Kion that is more open. Determined to discover what is scarring him, she devotes her time to seeing his point of view in his shattered world. While figuring out the balance in their lives and fighting for the other, Kion finally is confronted by the past figures of his high school days. Trying to put the traumas behind him, he and Ell help free the other from the barriers they have put up. Kion struggles to open up, find balance between Ell and his few and close friends, and, most of all, learn to love after guarding his heart for so long. Meanwhile, Ell must learn to trust herself, being reminded of who she is and is worth through Kion. Whenever Kion's greatest enemies, Dorcusso and Hellga arrive to seek their revenge though, Kion is faced with how strong his and Ell's love is, and whether it can truly stand and exist in that time. Facing death and unfortunate circumstances, the two prove how strong they truly are together in Peace of Mind.