Vampire Seon Woohyeol has one desperate wish: to become human and experience heart-pounding love. He tried many ways to become human, but none of them worked. After hearing from a 1000-year-old cat that he can become human if he sleeps in a hawthorn coffin for 100 years, he enters the coffin for a lengthy slumber.

With only one day left in his 100-year goal, he fails to become a human being. He is even bitten by a woman, Joo Inhae, causing him to faint. "Cat Man" Go Yangnam advises him to keep her by his side and watch her over, as she doesn't seem to be an ordinary person. Meanwhile, Inhae encounters a real estate scammer and gets involved in a chase to catch the fraudster, but finds herself in danger...

Inhae finds out that Woohyeol is a real vampire. However, what Woohyeol buys with her credit cards even makes her more shocked. She threatens to sell the mansion if Woohyeol can't repay his debt and starts living with him under a contract. Woohyeol reunites with two vampires named Lee Sanghae and Park Dongseop in the second-hand market. They lament the world in which vampires are drained by humans.

The blood on Inhae's lip triggers a memory in Woohyeol, reminding him of Yoon Haeseon. Woohyeol wonders if Inhae is the reincarnation of Haeseon. Inhae is concerned about her first kiss with Woohyeol and feels more uncomfortable seeing him, who is employed as a janitor at the school she works at. Cat Man tells Woohyeol that if he drinks Inhae's blood, filled with love, he can become human.

Woohyeol strives to turn Inhae's blood into full-of-love, but she shows no interest whatsoever. To make matters worse, rumors spread within the school that Woohyeol and Inhae are dating, which resulted in Inhae losing her job. Feeling upset, Inhae drinks heavily and confides her past to Woohyeol, and his genuine reaction makes her heart pound.

Inhae struggles to find a new job. Shin Doshik suggests Inhae start a guesthouse using her mansion. Although Woohyeol strongly opposes the idea at first, he eventually agrees because there is no other way for Inhae and Doshik to become closer. As Woohyeol realizes Doshik's affection for Inhae, he feels a pang of jealousy. Meanwhile, someone whom Woohyeol has longed for appears before him.

Woohyeol is surprised to see Na Haewon, who looks exactly like his past love, Haeseon. He can't approach Haewon because she doesn't seem to remember her past life. As Inhae feels sorry for Woohyeol, she invites Haewon to a dinner for Woohyeol to spend some time with her. However, Inhae becomes anxious, thinking that Woohyeol's vampire identity might be revealed during dinner.

Woohyeol and Inhae are forced to leave the mansion due to construction. Now that they are apart, they strangely think of each other more. However, Woohyeol starts experiencing physical symptoms and hears from Cat Man that if he doesn't consume Inhae's blood, filled with love, he will die from it soon.

Doshik discovers that Woohyeol is a vampire and tests Inhae, who unexpectedly protects Woohyeol. Woohyeol, troubled by the fact that he needs Inhae's blood to survive, faces additional challenges when Haewon becomes more affectionate towards him. Desperate to obtain Inhae's blood filled with love, Woohyeol's heart is tormented.

Inhae cannot understand Woohyeol, who says he needs to have her blood filled with love. Woohyeol proposes a deal where, if Inhae provided him with her blood, he would leave the house. Meanwhile, Haewon asks Inhae to throw a party to get closer to Woohyeol. Everything seems to go smoothly, but Inhae cannot shake off a sense of unease.

Woohyeol and Inhae develop strange feelings towards each other after the party. Doshik, who realizes something is going on between them, tries to take them apart by letting Inhae know that Woohyeol is a vampire. However, Inhae takes Woohyeol’s side instead. In a drunken state, Haewon calls Woohyeol, and while he's on his way to drop her off, he discovers a shocking truth.

While nursing Woohyeol, Inhae and Woohyeol confirm their feelings for each other. At Kim Gwangok's request, they spend time together while taking care of Kim Minjae. Meanwhile, Doshik, who is holding hands with Ri Manhwi, begins to suspect Woohyeol of being a half-vampire. Upon realizing that Woohyeol is aiming for Inhae's blood to become human, Doshik immediately sets out to chase after Woohyeol.

Woohyeol is unable to forgive himself for losing control due to his vampire instincts upon seeing Inhae's blood. As he suffers from the cruel fate that prevents him from being with Inhae, he decides to leave Inhae. Meanwhile, upon discovering that Woohyeol is the half-vampire he has been searching for, Doshik orders Manhwi to capture Woohyeol.

Inhae's long-awaited father makes a return, but her emotional wounds make it difficult for her to accept him. Meanwhile, Woohyeol's health continues to deteriorate, deeply saddening Sanghae and Dongseop as they realize that time is running out for him. Meanwhile, as Manhwi fails to capture Woohyeol, Doshik takes matters into his own hands.

Inhae's long-awaited father makes a return, but her emotional wounds make it difficult for her to accept him. Meanwhile, Woohyeol's health continues to deteriorate, deeply saddening Sanghae and Dongseop as they realize that time is running out for him. Meanwhile, as Manhwi fails to capture Woohyeol, Doshik takes matters into his own hands.

As Woohyeol accepts the fact that there's not much time left for him, he decides to spend the remaining time with Inhae. Doshik, upon finding out that Woohyeol is getting close to death, also becomes anxious. Will Woohyeol and Inhae be able to hold onto their love until the end?