That Thing Is A Virus.

Before Ji-min becomes a college student and gets a room, he comes to his old brother's house. Hyeon-soo found out about the fact late, but he is embarrassed, but feels at ease with Ji-min. However, Ji-min, who became a woman from a little girl, became more and more fond of her. But Ji-min had a boyfriend and Hyeon-soo tried to calm himself down, but while comforting Ji-min who broke up with his boyfriend, he heard that he was Ji-min's first love.