Resident Playbook: Who is Kim Sa Bi's HI-BOYZ bias Topkey oppa? Mystery solved as TXT and Kang You Seok light up MCountdown
One of the biggest cliffhangers in the medical drama is finally resolved—Kim Sa-bi’s favorite, Topkey, has been revealed. Find out who he is.

The penultimate week of Resident Playbook brought one of the show's most-awaited segments– the reveal of the members of Kang You Seok's former K-pop group, HI-BOYZ. The episode also marked the beginning of a budding romance between him and his OB-GYN colleague. When she revealed herself to be a fan, she mentioned her bias was "Topkey oppa," sparking curiosity about his identity. The mystery was finally unraveled on May 22, as the fictional group took the Mnet stage.
Resident Playbook's Kim Sa Bi (Han Ye Ji) showed an unexpected side to her character as she performed a HI-BOYZ song effortlessly alongside Um Jae Il (Kang You Seok) at a karaoke. While they danced, the choreography version of the song played in the background, featuring Um Jae Il and TXT's Yeonjun and Soobin. As Um Jae Il teased her about hiding her fangirl side while working with him, she revealed she was a fan of Topkey.
The revelation about which TXT member played the fictional Topkey was made during HI-BOYZ's appearance on MCountdown, when the members introduced themselves. It is none other than TXT's ace, Yeonjun. He introduced himself as "Go to the top. HI-BOYZ main dancer Topkey." Um Jae Il goes by the stage name Umjay and Soobin is known as DI.
Their respective positions in the group were also revealed by Namuwiki, with Topkey being the leader, main dancer, main vocalist and main rapper. The fictional group's MCountdown performance was nothing short of a real K-pop group act. For the ending fairy, Topkey made a cute gesture, indicating his name. He cracked up while doing so, creating an enduring moment.