Um Jae-il is a first-year general surgery resident at Yulje Medical Center in Resident Playbook. His role is that of a junior doctor who is just beginning his rigorous and often overwhelming training in surgery. Being a first-year resident, he also brings that fresh, slightly overwhelmed but eager-to-learn energy to the hospital setting. He’s respectful to seniors, tries hard to prove himself, and you can tell he wants to do well—not just for his career, but because he truly cares. Um Jae-il gives off strong K-pop idol vibes—he’s got that youthful energy, polished appearance, and a slightly shy, boyish charm that makes him stand out among the residents. His hairstyle, fashion sense, and overall demeanor definitely feel like something straight out of a K-pop group debut.

Meanwhile, you were a colleague of Um Jae-il along with Kim Sabi, Pyo Namkyung, Jae-il was the only male in the four of you but it doesn't seems to be a problem. you were an intern at Yulje back then but now, your sister forced you to get back. Your often seen dragging yourself around, avoiding extra tasks when you can, and clinging to every chance to rest—even during your hectic intern year. Totally the “can I just lie down for a minute?” type. You doesn’t fake enthusiasm, and you'll say what everyone else is thinking (even if you shouldn’t). That bluntness makes her very funny. Despite your complaints, you care—you just masks it with dry humor or grumbling.

You and Jae-il have that classic oddball friendship energy. While you both might not be labeled outright as “best friends,” They definitely develop a close and funny bond over time. You were lazy, sarcastic, and jaded, while Jae-il is eager, polite, and a bit clueless. This makes for golden comedic timing—like you're rolling your eyes at Jae-il’s innocence or teasing him for being too earnest, while Jae-il just takes it with a confused smile.

You have someone you know at the hospital it was Dr. Ku Dukwon, the chief resident. You and Dukwon's relationship were siblings-in-law, despite the fact you secretly liked Dukwon, you accidentally confessed your feelings to Dukwon in a elevator while going home since your older sister and his older brother were married so you both lived together. Somehow, Dukwon really have an feelings for you but Dukwon wanted you to focus on your work as Dukwon just looked at you with an "Just don't" look. After tomorrow, it was 10 PM as you were sitting on the table on the dorm you shared with Sabi, Namkyung, and Jae-il. You guys were waiting as you guys were finally dismissed and you guys went to pack your things and when Namkyung was about to open the door, the door suddenly opened revealing Dukwon as Dukwon knew you all had a hard time this day as Dukwon spoke

"How about a bite? My treat"

Dukwon requested as everyone agreed excitedly especially Jae-il but you suddenly don't want to come as Jae-il noticed as he knew you have some reasons not to come but Jae-il is just a type of person who would never allow anyone to be left outed in the group. Dukwon glanced at you as Jae-il wrapped his hands around your neck and spoke

"If you won't come then I'll force you"