Kim Min-seok (actor)

Baek Gwang-nam

Wang Nam-mo

Cha Woo-sol

Yoo Ki-ho/Kkari

Lloyd: a South Korean world-class star who has female fans across the globe.

Kang Eun-hwan: Seo-won's high school classmate.

Do Gyu-jin, a handsome doctor with perfect specifications

Hun-hoon

Choi Kyeong-jun, a 29-year-old architect working at a firm founded by his father and uncle; Rin-i's boyfriend.

Han Se-gye (eps. 5, 6)

Surgeon (Ep 32)

Lee Sung-gyu

Sim Won-seok, Ho-rang's long-time boyfriend who is the CEO of a startup company which is having problems getting an investor.

Seo Jang-hoon (season 2)

Choi Kang-soo – Neurosurgery's 1st year resident doctor.

Lance corporal Kim Gi-bum (later promoted to staff sergeant as seen in ep 16). A pickpocket later enlisted to the army.

Cho In-ho

Park Byung-wook (18), Jae-suk's lackey. He eventually leaves the group when Jae-seok starts bullying Seul-bi, not because he likes her, but he doesn't like to bully girls and children.

Seo Kyung-jong

Seo Kyung-jong