“I want you♥for my birthday gift.” On his 20th birthday, Joosuh Yoo declares he wants his long-time neighbor Hyunwoo Kang's body. Hyunwoo expresses that Joosuh's too young for him, but the passionate and headstrong Joosuh persists and Hyunwoo gives in for one night. After their night together, Hyunwoo continues to treat Joosuh like a child. Joosuh enrolls in college and is thrown into a new life. Hyunwoo is shocked after witnessing that Joosuh, despite being the kind kid Hyunwoo has ever known, is a total social pariah. When Hyunwoo asks why Joosuh isn't friendly to others, Joosuh remains steadfast. “You're all I need.” Hyunwoo has known the kid next door for a long time but contemplates how to take Joosuh's obstinate character to cling to one single person. Will Joosuh be able to win over Hyunwoo's heart?