Resident Playbook co-stars support HI-BOYZ on their M! Countdown debut

Hello Girls assemble! Resident Playbook's fictional K-pop group HI-BOYZ finally made their much-awaited debut on M! Countdown, a South Korean music program broadcast on May 22, 2025.

While the K-pop group is fictional and was formed as part of Um Jae-il's (Kang You-seok) character's back story, the group has gained much attention on social media platforms.

In Resident Playbook Episode 1, Jae-il reveals that he was a part of a K-pop boy band, HI-BOYZ, which disbanded in 2013, after which he applied for med school and became an OB-GYN resident at Yulje.

This lore was expanded in Episode 9 when Jae-il and the residents' squad go for a karaoke night. Jae-il plays HI-BOYZ's top charting song When The Day Comes on the screen behind him.

Fans were pleasantly surprised to learn that Jae-il's former band members were none other than TXT's Yeonjun and Soobin.

The K-pop group and their song became so popular that they were invited to perform on M! Countdown where You-seok was supported by his Resident Playbook co-stars, Han Ye-ji (Kim Sa-bi) and Shin Si-ah (Pyo Nam-Kyung).

Resident Playbook's K-pop boy band HI-BOYZ made their M! Countdown debut

While Resident Playbook did not feature a core group band like the parent series Hospital Playlist, it did feature a former boy band. Jae-il's backstory became so famous that fans started believing that the boy band is real.

While HI-BOYZ is a fictional K-pop group, it received real love from fans and they even made fan-chants like an actual group. In Resident Playbook Episode 9, other members of the group were revealed as TXT's Yeonjun (Top Key) and Soobin (D.I.).

When the Day Comes, Resident Playbook's OST released on May 11 is also sung by Yeonjun, Soobin and You-seok and it topped music charts for many weeks. The love this fictional K-pop group received on the show paved way for their reunion on M! Countdown.

In the May 22 broadcast, all the seven members of the group appeared for a special stage performance on their hit song, When the Day Comes. You-seok was even supported by his Resident Playbook co-stars Han Ye-ji and Shin Si-ah.

Both Ye-jin and Si-ah appeared as first year OB-GYN residents alongside You-seok.

HI-BOYZ appeared in color-coordinated blue and white outfits, and the fans chants and cheers were enough to tell how much fans love them and their song.

Ye-ji's character Sa-bi was also revealed as a Hello Girl (HI-BOYZ fan) in Resident Playbook Episode 9. The actress supported her co-star and even cheered for her bias 'Top Key oppa'. In addition, Ye-ji also participated in the When the Day Comes dance challenge with Yeonjun, which went viral on social media.

Fans of the group continue to treat HI-BOYZ like a real K-pop group and expressed their joy over their 'reunion'.

Playing along, Soobin commented on an X post: