Jisu Yoon is a survivor in the Green Roof Apartments
Jisu is somewhat tall (compared to other characters) with fair skin. She has red hair (sometimes perceived as red-ish brown) that is shorter at the back and longer in the front. Her eyes are light brown.Prior to the current time, when Haerang was alive, her hair was much longer.
Before the apocalypse, Jisu was shown to be a normal teenager. Jisu has been shown through multiple times in the webcomic as a confident and strong leader through tough situations. She is hard headed and speaks her mind on what is right. She is kind, accepting, and caring to others especially to Hyun Cha. She is a bass guitarist and likes to express herself through singing, songwriting, and playing the bass. Prior to the apocalypse, she played the bass every night, much to the annoyance of her neighbors.
After her boyfriend committed suicide, she valued life greatly and will do whatever she can to make sure others don't self-harm or take their own lives. She is very caring towards Hyun, and she was willing to sacrifice herself so that Hyun didn't turn into a monster. She is also protective of her bass guitar, which was given to her by Haraeng prior to his suicide and is the last memento of him.
Before present day, Jisu was dating and co-performing with a musician named Haerang. One night, the two sat by a river and discussed their most recent performance. Jisu had a much more positive opinion and attempted to console Haerang, who in turn gifted her a handmade guitar pick.
Later on, however, Jisu discovered Haerang hung himself and left her his bass. The shock and emotional trauma of this led Jisu learning to greatly value life. She eventually moves into Green Roof Apartments, taking residence in room 1510. She has a tendency to play the bass too loud at night, irking her neighbors.
At the initial outbreak at Green Roof, she was playing her bass loudly in her room. This, unfortunately, attracted the attention of the Hungry Monster. She is terrified of the monster's appearance and attempts to break into her apartment. However, Wook Pyeon arrives and the monster jumps out the building to its death. Wook and Jisu then check in on Hyun Cha, who passed out from early monsterfication symptoms. Jisu notes that they can't get in touch with security and wants to go check the guard's office. Wook volunteers to go instead out of concern for Jisu's safety. However, after noting how long Wook was taking, she grabs a baseball bat and begins making her way downstairs. She runs into a strange man muttering to himself and tries to ignore and pass him. However, the man notices her and begins to monsterfy, forcing Jisu to knock it out. Jisu still is not aware of the apocalypse and tries to check in on the man, but she was saved by Jayhun before the monster attacked.
She hides out with Jayhun in room 1107, its previous occupants suffering an unknown fate, for safety. They two eventually hear a Hyun vs. Steroid Monster vs. Blind Monster and rush to help the survivor. However, Jisu is then scared to learn that Hyun is infected and is initially mistrustful of him. She nonetheless agrees to help Hyun save two young children from the Steroid Monster. She eventually does so and they all meet in Dusik Yang's apartment. She is still mistrustful of Hyun and the new infected survivor they met, but she attempts to lighten the mood. However, she cautiously watches Hyun at night while on guard duty, even beyond her normal watch time. She learns that Hyun has lost everyone who would have grieved his death. She is then shocked to learn that Hyun has been practicing self-harm, and firmly encourages him to end that habit.
After a few days, Jisu, Hyun, and Jayhun decide to find a way to escape the apartment. Hyun also wants to meet up with other survivors he suspects is on the first floor. They do not make it very far, however, as they eventually have to survive an attack from the Tentacle Monster. They are saved by the arrival of the rescue party from the first floor. Jisu then sticks up for Hyun as the rest of the survivors are too mistrustful of Hyun's infection and are considering throwing him out. After Hyun is accepted, he is sent on a mission with Wook to rescue Dusik. Jisu is furious at Hyuk Lee for sending only a two man squad, but Hyuk explains that he took a gamble on Hyun's ability to quickly recover from injuries as a factor for the mission's success even going as far as preparing to rig the vote in Hyun's favor. However, Hyuk noted that 6 people voted of their own will to accept Hyun around, noting that it is highly unusual for a band of survivors to accept an infected stranger. This heightens Jisu's paranoia of the people around her, especially after seeing Seon An's telltale signs of infection. Jisu confides with Jayhun that she believes the people who voted to accept Hyun were also infected, but they couldn't figure out who since the vote was anonymous. Jisu and Jayhun decide their best chance at survival was to leave, but Hyuk tells them the parking garage has been breached, meaning they will be unable to leave safely.
Jisu (tried to) warmly greet Hyun upon his return. She learns what happened to Myeong-An from Wook, and is inspired to write a new song. They are interrupted by a few other survivors, who explain that Mr. Kim has turned into a monster and is killing anyone who didn't make it to safety. Byeong-Il and another survivor attempt to keep the room barricaded, even preventing Jisu and Hyun from running to help. Jisu threatens Byeog-Il with violent force if the two don't cooperate, which they do. The two get to the main lobby, and are horrified to discover Mr. Kim had brutally killed Jayhun. Jisu attempts to fight back, but is easily knocked aside. She is shocked and horrified to see that Hyun is edging closer to becoming a monster, and desperately tries to snap him out if it. Her pleas reach Hyun, who comes to his senses and finds a way to defeat Mr. Kim.
She is part of the team sent to kill all the monsters in the garage. Unfortunately, the "monster" she kills turns out to be a decoy, and she gets ambushed by the Upside Down Face Monster. She barely dodges, but took on a bad shoulder injury in the process. Jisu, therefore, is unable to participate in a mission to get more supplies from a grocery store. She insteads attempt to see Hyun off, but is forced to assist when the Steroid Monster immediately destroys the vehicle.
Jisu and the survivors are put in further danger when Byeong-Il attempt to take over the apartment. She is further horrified at the tyrranical methods the gang uses especially towards monsters. However, she is forced to obey in order to survive. Jisu is disappointed when Hyun decides to help the criminals. Eventually, she tries to find Hyun to apologize, but learns he has gone with Ihyun Jo to destroy the other monsters. She meets up with Hyun in Dusik's old room, and is shocked to see that the Infant Monster transformed into a mysterious cocoon. As she and Hyun debate what to do, Ihyun incinerates the egg. Unfortunately, this attracts a large amount of monsters to the area. A Flying Monster grabs and tries to fly off with Jisu. As Hyun tries to save her, Jisu notices Hyun is giving in to his monster side. With her attempts to reach Hyun failing, Jisu decides the only way to keep Hyun human is to sacrifice herself. Hyun, however, snapped back to his senses upon seeing this and frees Jisu by impaling her with his electric spear, which shocks both her and the monster. The two attempt to make up, but have to quickly run from the recovering monster.
As Hyun and Jisu make their way to the ground floor, they witness Joon Shin, the criminal leader, kill a survivor. Joon Shin then takes Jisu hostage, threatening to kill her if Hyun attempts to attack him. However, Hyuk attacks Joon from behind, forcing him to release Jisu. Jisu is shocked to see Hyuk is showing signs of being infected, but is quickly forced to flee when Hyuk tells her that the lobby is being overrun by monsters. She runs to find her bass guitar and the young children. She and Hyun meet up with some other survivors on the 11th floor. When Hyun learns of Dusik's sacrifice and runs off to save him, Jisu tries to follow, but is stopped by Hyuk, who assures Jisu that Hyun can take care of himself. As they make their way toward the roof, Hyuk notes that it is unusual for monsters to leave their initial territory and gather in one location like just now. Jisu wonders if the survivors missed something about the monsters and may have messed with something important to them, reflecting on incinerating a cocoon and killing the mysterious woman.
As they continue up the stairs, Jisu reflects on the current situation and silently slips away from the rest of the group before anyone notices. She goes back to her apartment building, contemplating how to build hope. As she reflects on her time with Haerang, she prepares her bass and speaker, intending to create a lot of noise to distract the monsters and fully aware the plan is likely to end with her death. She begins playing the bass and successfully attracts the monsters' attention. She is surprised when Hyun suddenly breaks in through the apartment window, and is alarmed to see he is turning. However, she is forced to shift her attention to defending against the monster horde breaking down her door.