Vampire Seon Woo-hyeol 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, In-hae, causing him to faint. "Cat Man" Go Yang-nam advises him to keep her by his side and watch her over, as she doesn't seem to be an ordinary person. Meanwhile, Joo In-hae encounters a real estate scammer and gets involved in a chase to catch the fraudster, but finds herself in danger...

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

The blood on In-hae's lip triggers a memory in Woo-hyeol, reminding him of Yoon Hae-seon. Woo-hyeol wonders if In-hae is the reincarnation of Hae-seon. In-hae is concerned about her first kiss with Woo-hyeol and feels more uncomfortable seeing him, who is employed as a janitor at the school she works at. Yang-nam tells Woo-hyeol that if he drinks In-hae's blood, filled with love, he can become human.

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

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

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

Woo-hyeol and In-hae are forced to leave the mansion due to construction. Now that they are apart, they strangely think of each other more. However, Woo-hyeol starts experiencing physical symptoms and hears from Yang-nam that if he doesn't consume In-hae's blood, filled with love, he will die from it soon.

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

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

While nursing Woo-hyeol, In-hae and Woo-hyeol confirm their feelings for each other. At Kim Gwang-ok's request, they spend time together while taking care of Kim Min-jae. Meanwhile, Do-shik, who is holding hands with Ri Man-hwi, begins to suspect Woo-hyeol of being a half-vampire. Upon realizing that Woo-hyeol is aiming for In-hae's blood to become human, Do-shik immediately sets out to chase after Woo-hyeol.

Woo-hyeol is unable to forgive himself for losing control due to his vampire instincts upon seeing In-hae's blood. As he suffers from the cruel fate that prevents him from being with In-hae, he decides to leave In-hae. Meanwhile, upon discovering that Woo-hyeol is the half-vampire he has been searching for, Do-shik orders Man-hwi to capture Woo-hyeol.

In-hae's long-awaited father makes a return, but her emotional wounds make it difficult for her to accept him. Meanwhile, Woo-hyeol's health continues to deteriorate, deeply saddening Sang-hae and Dong-seop as they realize that time is running out for him. Meanwhile, as Man-hwi fails to capture Woo-hyeol, Do-shik takes matters into his own hands.

In-hae's long-awaited father makes a return, but her emotional wounds make it difficult for her to accept him. Meanwhile, Woo-hyeol's health continues to deteriorate, deeply saddening Sang-hae and Dong-seop as they realize that time is running out for him. Meanwhile, as Man-hwi fails to capture Woo-hyeol, Do-shik takes matters into his own hands.

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