Park Seo-joon

Song Min-soo, an actor (Ep. 9–10)

Lee Young-joon / Lee Sung-hyeon Moon Woo-jin as 9-year-old Lee Sung-hyeon

Ko Dong-man Jo Yeon-ho as young Ko Dong-man

Moo-myung / Kim Sun-woo / Kim Isabu / Dog-bird

Ji Sung-joon Yang Han-yeol as young Sung-joon

Oh Ri-on (Omega / Oh Hwi) Kim Ye-jun as child Oh Ri-on

Adult Geu-roo

Yoon Dong-ha

Song Min-soo, Mi-kyung's half brother

Park Hyun-tae The carefree and happy-go-lucky youngest son of Park Soon-sang. His biological mother Min Young-ae, another of Sang-soon's mistresses, chose to send him to live with his father for financial reasons and better prospects. While growing up he learned to keep a low profile so that he won't be thrown out by Deok-hee, who despises him and treats him coldly. He is coddled by his father and older brothers and longs to experience life outside of the wealthy upper-class circle that his family belongs to.

Cha Seo-joon

Lee Si-woo