Yui arrives in the mysterious house and meets the six brothers who are actually vampires but none of them knew about her arrival except Shu who explains that he received a call the other day from a man and he told him to keep her safe and not to kill her. Soon, Yui learns that she is the prospective bride and she tries to run but ends up in an abandoned room where she finds her dad's diary and discovers that she is adopted. The episode ends with Yui yelling for help as she was cornered by the six brothers.
It is the first day at a new high school for Yui but she finds it strange that the high school is at night. On their way to school she notices that all the brothers are different from each other and don't seem to get along. Later at school Ayato forces himself on Yui and sucks her blood and does not stop until Reiji comes and tells him to take his activities to his private room. Later, Ayato throws Yui in the swimming pool and orders her to say that he is great but Yui can't swim and asks for help. Ayato then has a flashback of his childhood and after that he jumps in the pool to save Yui. He kisses Yui underwater to wake her up and suck her blood; Yui begs him to stop and he stops, telling her he will continue later. At the end of the episode Yui goes back to the abandoned room to see her dad's diary but finds it blank and is confused.
Yui eventually learns that the brothers are different from each other, since they all have different mothers, Shu and Reiji have the same mother, Ayato, Kanato and Laito are triplets from another mother, and Subaru has a different mother. After Yui grabs Shu's hand, an old memory comes into his head. When Shu sees that he held Yui's hand tight, he drags her to the tub and says he wants to suck her blood (possibly make her hate him so she's not too attached to him). Yui is shocked to think he was different, but he tells her he's a vampire. Later that night Ayato also tries to suck Yui's blood, but is annoyed to find bite marks on her neck, Ayato challenges Shu to play darts with Yui as the prize. Shu wins the match and is about to leave, Laito pushes Yui towards him.
Yui tries once again in vain to try to contact her father, but is stopped by Kanato, who later decides to hide her backpack on the roof of the school as "punishment" for not bringing him the accommodations that he had asked for. As Yui goes to retrieve her belongings, she stumbles upon Laito, who seems to be citing strange words to the moon.
Kanato finds Yui in the rose garden as she tries to sort out the new information about who betrayed her and gave her up as a sacrifice. He beckons her to follow him so he may show off a graveyard containing the grave of his mother. Assuming he would like some time alone, Yui attempts to leave which only infuriates Kanato with misplaced anger. Reeling from this experience, Yui wanders through the estate, and becomes worried when she hears groans coming from Reiji's room. Much to her folly, she enters the room to see if he needs help.
Yui refuses to accept that she should suddenly stop showing compassion towards the brothers merely because they are vampires, and allows herself to be led to one of Kanato's most favorite places in his little world. As she views his family's collection of wax figures all in bridal wear, she finds herself eerily aware that things are not as benign as they appear. Kanato confirms her suspicions and gleefully sets to adding her to their collection, until he is interrupted by a summons.
Yui is awakened by the sound of rain and looking from her window, she sees a mysterious woman in a purple dress. She becomes controlled by an unknown force, and goes all the way to a secret tunnel and through a door that leads to the past. There she sees the brothers as children. But after she discovers the truth of their past, she reappears in the tunnel and is found by a concerned Ayato, who instructs her not to return down there, especially during the rain.
Yui asks the triplets about the woman in the purple dress who she spotted in the garden, and learns the gruesome truth about what befell their mother. Yui runs out of the house in horror and collapses sobbing in the garden, only to be approached by Subaru, who demands she keep her distance from him, or else. Yui spends a sleepless night in her chamber, made less restful by the arrival of an unwanted guest.
Yui experiences more chest pains and leaves the mansion in the middle of the night to seek answers and finds Shu in an abandoned church. At first, he is unhelpful but quickly becomes interested in obliging her request for answers by forcibly tasting her blood to verify that is has indeed changed somehow. Richter then appears and takes Yui to the secret room where 'Cordelia' awakens and everyone feels it especially Ayato who goes to find her, to end up finding Yui's rosary on her bed.
Cordelia and Richter savor one another's company for the first time in ages, until Ayato interrupts, demanding to know what they have done to Yui.
While Cordelia and Richter catch up, Reiji appears, and Cordelia begins to tease him in a seductive way. He then rejects her, and Laito, Kanato, Subaru, and Shu all appear due to the commotion. As they discuss the situation, she gives a knife to Richter so he can "dispose" of all the boys for her. Richter does not follow suit, as it is revealed that he had been using Cordelia to further his plan of becoming head, much to her chagrin. Going after her heart, Ayato appears and tells the two to end the bickering, and that Yui belongs to him. As he and Richter duel in attempt to win Yui, Ayato is stabbed. Just then, Yui regains control of her body, and calls for Ayato. She then stabs herself in the heart in order to save everyone. Richter attempts to take Yui's heart, but is stabbed by Ayato. At that moment, Cordelia takes over Yui's body once more.
Returning from when Yui stabbed herself, Subaru takes out the silver knife. Richter then struggles to the attic where he has hidden Cordelia's dress, however Laito finds him there and prevents him from using the dress to keep him alive. Meanwhile, Shu, Subaru, Kanato and Ayato are watching over Yui and the awakening takes place. Reiji makes a potion to kill Cordelia while she's in Yui's body, but in order to make the potion complete, he must have a piece of Cordelia. Kanato pulls Teddy apart to reveal a vial containing Cordelia's ashes and this makes the potion complete. Switching back to the attic, Laito sets fire to the dress and Richter, which then the fire kills him. Ayato then drinks the potion only to feed it to Yui through a kiss and calling her actual name. Yui then awakens, and notices all the brothers are with her. She then sits up and with a thoughtful look she says "I'm so thirsty", indicating that she turned into a vampire, and that she is thirsting for blood. After the credits end, we see all the brothers talking to Yui, one-by-one. Resuming the episode, we see Yui on the balcony holding a rose, Ayato then walks up to her a returns her cross necklace. We then see the rose falling and the petals falling off, and chains locking Cordelia in the attic.
