A younger brother who lives with his older brother's girlfriend! Young-ho and Seo- yeon, who met and became lovers a year ago, and Sang-a and Jae-hoon, who became lovers on the same day. Youngho and Jaehoon are brothers who have been living together for a long time. Seo-yeon, Yeong-ho's lover, recently moved into the brother's house and lives with them. Living together, Jae-hoon and Seo-yeon fight over trivial matters almost every day. We fight too often, and sometimes Yeong-ho gets angry, but he lives happily ever after. Jae-hoon is also not very dissatisfied with his life with Seo-yeon, but he is tired of Yeong-ho and Seo-yeon's intense relationship. In fact, whenever I see Sang-a, Jae-hoon's girlfriend Sang-a, who is having a hard time seeing her because of her doctoral course, I envy the Young-ho couple. Meanwhile, Jae-hoon has a strange dream of having a relationship with Seo-yeon... Can these two couples be able to maintain their relationship?