Sol Ah has feelings for Jae Seon, but one day, Jae Seon disappeared without saying anything. It turns out Jae Seon has been dating a new rich girlfriend whom he recently broke up with, leaving him with the cat he gave her as a gift. Because of Jae Seon’s cat allergy, Sol Ah somehow ends up taking the cat home.

Things would’ve been detrimental if Hong Jo hadn’t been there when Sol Ah’s dad, Soo Pyung, fainted in his apartment. Sol Ah, at the hospital, finds out about Soo Pyung’s illness and also meets his fiancée for the first time. Now that Sol Ah has to move into a new house to live alone, she feels somewhat reassured that Hong Jo is by her side although she still hates cats.

Sol Ah moves to a new place on her own. It’ll be her first time living alone and she’s feeling mixed emotions about it. With high hopes, she arrives at her new house and is surprised. She’ll be neighbors with Jae Seon, her first love and crush.

Sol Ah starts drawing webtoons again at her new place. Hong Jo continues to orbit around Sol Ah living a double life. One day, Hong Jo accidentally saves Sol Ah and becomes her life-saver. Things seem to be settling down, but there's something fishy about the new house. Is there someone else living with Sol Ah and Hong Jo?

Sol Ah gets a call from Sil and thinks Hong Jo is Guk Bong. Doo Sik and Jae Seon come to Sol Ah’s home to give a warning to Hong Jo, but they can’t find Hong Jo anywhere. Sol Ah asks Jae Seon why he ran away, but he only says sorry to her. Meanwhile, Sol Ah uploads “Helpless Beodul Love” Episode 1.

Doo Sik gives Sonamu’s free coupon to Ji Eun, and Ji Eun goes to Sonamu. Doo Sik brings Hye Yeon and Da Som to Sonamu, and they encounter Ji Eun there. Sol Ah and Doo Sik realize that Ji Eun was also a member of the art club. Meanwhile, Sol Ah tells Jae Seon to stop making her confused.

Sol Ah tries to move on from Jae Seon and goes on a blind date. At the meeting spot, she finds Guk Bong and realizes that Doo Sik set her up with Guk Bong. The two enjoy the afternoon anyway and come back home with fun memories. However, Jae Seon breaks the news to Sol Ah. He found someone who will take Hong Jo.

Sol Ah and Hong Jo both feel perplexed as Sol Ah decides to send Hong Jo off. Hong Jo feels like he’s being abandoned and Sol Ah feels like she’s letting off a good companion. Hong Jo never wished to be a human being so badly. On the day of meeting the new owner, Hong Jo disappears and Sol Ah roams around all night to look for Hong Jo.

Sol Ah thinks Hong Jo is dating Ji Eun. Jae Seon realizes that he misunderstood Sol Ah and apologizes to her, but Sol Ah doesn’t accept his apology. Sol Ah and Ji Eun become friends and have a drink together. Sol Ah encounters Guk Bong, but she still thinks Hong Jo is Guk Bong.

Ji Eun and Sol Ah become friends and Sol Ah gets to know Ji Eun’s true feelings about Doo Sik. Doo Sik who is oblivious about Ji Eun’s interest in him and thinks she’s the only one who hates him at work. It provokes him and he tries to persuade Ji Eun to like him.

Jae Seon finds out that Guk Bong is actually a cat. He’s Hong Jo. Hong Jo asks Jae Seon to keep it as a secret from Sol Ah because he wants to be by her side. In return for keeping his promise, Hong Jo begins working as a part-timer at Jae Seon’s café.

Sol Ah waits for Hong Jo, but he doesn’t show up because he gets abducted. Sol Ah and Jae Seon start searching for Hong Jo. Hong Jo apologizes to Sol Ah for not showing up that night. Sol Ah worries that Hong Jo might disappear again, while Jae Seon is not happy with this situation.

Hong Jo thinks drinking coffee will help him stay awake. Hong Jo tells Sol Ah that he can stay up all night with her if she wants. Embarrassed, she sleeps over at Ji Eun’s place instead. Hong Jo tells Sol Ah that he will not stay at home if she feels uncomfortable. Meanwhile, Hong Jo gets to know Sol Ah’s feelings for him.

Hong Jo finds out that his time as a cat passes by more quickly than if he was human. Cats age faster than humans and that will eventually lead him to die before Sol Ah. He realizes he doesn’t have much time to stay by Sol Ah’s side. After much contemplation, he decides to leave Sol Ah rather than to tell her the truth about himself.

Jae Seon is jealous of Hong Jo and Sol Ah growing closer to each other. He realizes his true feelings toward Sol Ah and wants Hong Jo to be gone as soon as possible. On the day Sol Ah was to go to her father’s house, Jae Seon goes to the train station to tell her that Hong Jo, Guk Bang left. He also tells her that he’ll always be by her side from now on.

Hong Jo tells Sol Ah that he is Hong Jo, but Sol Ah doesn’t believe his words. Jae Seon warns Hong Jo to leave, but Hong Jo doesn’t want to leave Sol Ah just because he is afraid of being abandoned. Sol Ah gets to meet the real Guk Bong and is confused about Hong Jo’s identity.

Ji Eun and Doo Sik have dinner together at his parents’ restaurant. Ji Eun tells Doo Sik why she likes him. Jae Seon tells Sol Ah about his sad childhood story, and Sol Ah feels sorry for him. Jae Seon tells Sol Ah that he will stay by her side. Meanwhile, Sol Ah tells Hong Jo to give her some time.

Hong Jo stays with Jae Seon and the two noticed an old cat that has yet been adopted. Hong Jo keeps asking Jae Seon if he really has nobody to ask the favor of adopting a cat. Jae Seon reluctantly heads to his parents' house, the house he walked out years ago with Hong Jo. The two finally meet Jae Seon’s father in person and are both surprised.

Hong Jo shares his last secret to Sol Ah. As a cat, his time will go faster than Sol Ah’s, making him grow older fast, and eventually, die fast. He boldly shares how he already made up his mind in deciding to stay by Sol Ah’s side, no matter what. Now, he leaves it up to Sol Ah to make her final decision about their relationship.

Doo Sik tells his parents that he is in a relationship with Ji Eun. Sol Ah gets an offer to publish her webtoon officially. Sol Ah is busy, and Hong Jo is a bit sad thinking that he isn’t part of Sol Ah’s happiness. Meanwhile, Ji Eun tells Doo Sik that he is so tactless to tell everyone about their relationship.

Hong Jo waits for Sol Ah. Sol Ah tells Hong Jo that it makes her hard if he keeps waiting for her. The time Hong Jo can spend as a human is predestined, and it is getting shorter and shorter. Ji Eun draws a new sign for Doo Sik’s parents’ restaurant. Meanwhile, the animal hoarder is back.

Hong Jo’s time is running out as he can’t transform as often as he used to. Jae Seon’s father passes away and he sadly recounts his short, last days with his father. Sol Ah realizes she really does not have much time left with Hong Jo and decides to quit her job to stay at home with Hong Jo.

The longer Sol Ah stays only at home, the more Hong Jo becomes worried about her. He wishes only the best for her and encourages Sol Ah to live to the fullest as herself. One day, Hong Jo wakes Sol Ah to say his last words. This might be his last moment living as a human being.