Im Shin Yoon, who lived his whole life as the eldest son of the Im family with four sisters full of personality, finds out at family dinner that Nam Chae-gwan, a mysterious chaebol who’s the best friend of his parents and lived a life of fortune isn’t just a really good friend of his parents. Nam Chae-gwan happens to also be his biological dad! Which makes Shin-Yoon the son of "Nam," so he receives an absurd proposal from Nam Chae-gwan, which makes his relationship with the four sisters unclear...