After Yumi brought up the topic of marriage, their relationship grows awkward for some reason. Meanwhile, Woong and Ba-bi attend the same dinner party by coincidence, and drunk Woong forgets everything that happened that night. What could have happened the night before? Woong feels anxious all of a sudden...
At a friend's wedding announcement, Yumi mentions that she has a boyfriend. When her friends don't believe her, she proclaims that she will bring Woong to the wedding. But Woong is too busy, she has no choice but to... Just as she was about to give up, another situation crops up where it becomes necessary that Woong attends the wedding.
Having only dreamt of it, Woong finally visits Yumi's house. That night, Yumi and Woong spent an unimaginable night together. At Woong's suggestion, the two of them decide to go on a trip. Yumi's heart races at the thought of a hotel stay with an ocean view, even though her Travel cell is dead. Also Naughty Cell's heart is racing, too...
Cells live inside Yumi's head, a 32 year-old who works at Daehan Noodles' finance department. In her dull life where her main concerns are what to eat or wear, only one thing excites Yumi and her cells — Woo Gi from Sales! He's handsome, gentlemanly, and 5 years younger... Age doesn't matter if he's just a crush, right? Or she thought, but Woo Gi keeps hanging around her. Is this a green light?