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Resident Playbook, a new medical drama was released on April 12, 2025, on tvN and Netflix. However, what caught fans' attention was the fictional boyband, HI-BOYZ, which is at the center of the show. Resident Playbook follows four inexperienced residents at Yulje Medical Center's Jongno branch, aspiring to become surgeons, despite their daily struggles.
Fans of the show have made several theories about the lives of the fictional band members after they disbanded in Resident Playbook. First-year resident Um Jae-il or Um Jay (Kang You-seok) was a former member of HI-BOYZ. The series shows that after his band broke up, he decided to study to become a surgeon. Known by his stage name Um Jay, the show depicts him starting his residency after medical school.
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The band, HI-BOYZ, debuted on February 4, 2011, but disbanded on December 28, 2013. Over the course of their career, the band did get recognition and praise for their song, When the Day Comes. The other members of the band were portrayed by Kang You-seok's TXT band members Yeonjun and Soobin.
The short cameo appearance of TXT members had fans excited as they had a lot of questions about HI-BOYZ. However, a lot of information about either Soobin's or Yeonjun's characters was given in the drama.
That being said, fans used the fact that Soobin and Yeonjun are part of TXT, an active K-pop group, to create theories surrounding their fictional boyband.
One of the fan theories suggested that Soobin and Yeonjun trained at BIGHIT MUSIC and joined the lineup of TXT, re-debuting in 2019. Yeonjun was known as the ace trainee, while Soobin gained praise for his vocal and leadership skills.
As per the theories, Soobin became the leader of the BIGHIT MUSIC group, and Yeonjun is recognized as the “IT Boy.” Fans shared their thoughts regarding the fictional group's activities following separation.
"Then Jaeil studied hard to become a doctor while Soobin & Yeonjun joined a bigger company to re-debut as Tomorrow X Together that’s a complete lore right there..," a fan wrote on X.
"Doctor while Soobin & Yeonjun joined a bigger company to re-debut as Tomorrow X Together. That’s a complete lore right there," a user stated.
"after his-boyz disbanded, yeonjun became a bighit trainee the following year, and soobin joined 2 years later. they redebuted with txt in 2019 and now become the popular groups," a netizen said.
Fans highlighted the possible reason behind HI-BOYZ's disbandment could be that the makers of the show forgot about the rest of the members of the band. It is worth noting that Resident Playbook has yet to clarify whether the other members of the band are a part of the group or background dancers.
"screen time for only 3 members, only 3 members got the centre AND 3 ghost singers this is exactly why hi-boyz disbanded," a fan commented.
"Those four other members feel like back dancer with outfits and make up," another fan commented.
"Omg I cant believe you didn't include the rest of the members..... we have to STOP the ot3 stans, OT7 FOREVER!!!," a netizen wrote.
Meanwhile, for the theory to be real some Resident Playbook fans also imagined how old Soobin and Yeonjun would be if they were a part of HI-BOYZ and then TXT. They expressed their sadness about how the idols would have been young boys when their band started.
"Yeonjun and Soobin are 12 and 11 years old here," a user stated.
"soobin and yeonjun were only 11 and 12 yrs old when they first debuted," a netizen said.
"realistically speaking, that would mean Yeonjun & Soobin debuting at the ages of 12 & 11," a fan mentioned.
Who is Top Key? Kim Sa-bi reveals her favorite member from HI-BOYZ in Resident Playbook
In Resident Playbook episode 9, Um Jae-il learned that his fellow resident Kim Sa-bi (Han Ye-ji) was a Hello Girl and fan of HI-BOYZ before their disbandment. After learning that, he asked her how she held back for so long since she was his fan.
Kim Sa-bi nonchalantly responded that she wasn't his fan but a fan of another band member named Top Key.
Notably, Resident Playbook focused on Um Jae-il, but it was not shown who Top Key was. In reality, actress Han Ye-ji did the When the Day Comes challenge with TXT member Yeonjun and that was when she mentioned that he was Top Key.
Fans and viewers quickly noted that Top Key was indeed Yeonjun. However, information about Soobin's character has not been shown in detail.
Resident Playbook has entered the final week of airing and will release episodes 11 and 12 on May 17 and 18, 2025, respectively, on tvN and Netflix.
