Yoon Ju-won is a bright, down-to-earth girl who lives with her single father, Yoon Jeong-jae, when Kim San-ha and Kang Hae-jun, two boys from complicated circumstances, come into her life. Her father takes in the boys to grow up together as a family. Despite being unrelated by blood, Ju-won adores San-ha and Hae-jun and thinks of them as her brothers, no matter how differently others think or say. They reunite after a decade apart - facing new dynamics, unresolved pain and the complexities of adulthood.