In the opening scene of Episode 3 of Yumi's Cells Season 3, we find Soon-rok attending a baseball game for one of the writers he manages. The episode paints a vivid picture of Soon-rok as a person whose energy dwindles in the presence of others. To conserve it, he operates in a low-power mode, where only his Rational Cell takes the reins. This explains his abrupt behavior with Yumi and the infamous headphones incident.
After an exhausting movie marathon with Ahn Dae-young and another writer, Soon-rok heads to his meeting with Yumi. His battery already depleted, he can only discuss Maltese dogs, unaware that it upsets Yumi. When he returns home, his cells awaken, and his senses come alive. The narration reveals that he's a total homebody who cherishes baseball and movies from the comfort of his home. He's even able to provide Yumi with better feedback.
That's why he's annoyed to learn that he has to embark on an unplanned weekend trip to Busan. He rushes to catch the train and, seeing as he looks like a mess, decides to sit far away. This brings us back to the present, where Yumi questions him about leaving the team. At that moment, Soon-rok's battery is completely drained, and he simply smiles at Yumi. In Yumi's cell village, lightning strikes!
Soon-rok then receives a phone call from PD Jang and steps away to speak to her. Unfortunately, the train starts moving before he realizes. He sends Yumi an apology text and says he'll take the next train. In Yumi's cell village, the cells discover that the lightning killed all the angry snappers. Which means she wouldn't be angry anymore. They investigate the source of the lightning and realize that one cell has woken up from the freezer pods—the Love Cell!
While sitting alone at the train station, a part of Soon-rok's battery gets restored. Meanwhile, Yumi waits for him with both of their bags. When she spots him in the crowd, lightning strikes the cell village again. Soon-rok finally explains that the change in management is purely due to overlapping schedules and not for any other reason. However, Yumi feels a spark when his hand brushes hers.
The Busan event proceeded smoothly, and the episode swiftly shifts to Yumi returning to her studio. On the surface, she appears calm, but internally, her cell village has been ravaged by lightning strikes.
Na-hui brings a cake to the meeting to celebrate Soon-rok's birthday. Yumi breaks the news to her about the change in PD, and Na-hui decides to send him a message instead. He calls her back and says he might stop by since he's nearby. Yumi's heart begins to race at this news.
When Soon-rok arrives, he gives Yumi a framed photo from the Busan event. Na-hui brings out the cake, and Yumi is shocked to learn that he's only 29 and lives alone. Na-hui points out that he's talking more than he usually does and suggests it's because he's not there for work but for a personal reason. He then reveals that he's going to a publishing workshop in Busan that evening, and Yumi was invited as well but chose not to go.
Meanwhile, Writer Cell has been getting frustrated at how the other cells are thinking about Soon-rok. Now, he gets even more frustrated when Yumi cuts her writing session with Na-hui short. As Yumi makes the decision to go to Busan for the workshop, Love Cell shows up in Writer Cell's tower and tells him she's taking back the Prime Cell position.
Yumi heads to the train station, where PD Jang calls her and tells her that Soon-rok will be on the same train as her. As he greets her and takes her bag, Yumi admits to herself that she likes Soon-rok. In her mind, Writer Cell is put in handcuffs. But he argues that Soon-rok doesn't even like Yumi back. On the train, Soon-rok puts his headphones on again. But this time, Yumi smiles. Love Cell tells Writer Cell that it doesn't matter; she's awake now, and Yumi's dull existence is over.
