Reiji makes his first appearance when he interrupts Ayato from biting Yui. He tells Ayato that he should take such activites to his private room. When Yui asks him for help, he questions her identity. When Yui tells him that her father told her that she'll be living here, Reiji responds with how he didn't hear nothing of the sort, and asks Ayato to explain this to him. He comments on how this is strange since he hasn't been informed about this. Reiji then says that they should discuss this elsewhere, ordering one of their butlers to see to her luggage. When his other brothers start to lick Yui, he scolds them by saying that such behavior is impolite towards a young lady they've just met. He then asks them if anyone has been told about Yui living there with them. Yui claims that this is a misunderstanding and starts to leave, but Reiji stops her by saying that he's attempting to verify the truth of the matter, and that it would be impolite of her to leave now. Once his elder brother, Shu, clears up the misunderstanding, Reiji tells her that there isn't one and proceeds to introduce everyone. When Yui realizes that they're all vampires, she pulls out a cross. Reiji sits down and asks her if she really believes that vampires are vulnerable to garlic, holy crosses, and sunshine. He then comments how this goes to show how foolish and arrogant mortals are and how it makes him furious. Yui runs out and he says that her manners are deplorable. He then appears in the room Yui ran off into with his other brothers, saying that out of all the rooms she could've entered, she just had to choose this one. He explains that this is a room that they sealed off so no one may enter, and now he'll have to fit it with a new lock. Reiji then tells her that there's only one fact she must comprehend, the fact that she can never escape from them.
Reiji interrupts Ayato and Laito who're arguing over Yui. He informs them that they'll be late and tells Yui that she needs to get changed. When Yui questions why, he rudely asks her if she needs everything to be spelled out for her, then explains they're going to night school, and that they cannot allow her to be active during the daytime just because she has the common sense of a mortal. He says that as long as she lives in the Sakamaki residence, she must adjust to their lifestyle and if she has a complaint, she is free to leave at any time. He tells her to hurry up and dress into her uniform. Next scene, all of them are seen in the limousine. When Ayato is about to bite Yui, Reiji once again interrupts him by saying that he should take such activities to his room. He then tells Yui that the cranberry juice is for her, explaining that it's the best cure for weak blood. Yui thanks him, and he responds by saying he shouldn't thank her and she must be fully aware that she is their prey and drink that daily. Once they arrive at the school, he explains to her that she's in the same class as Ayato and Kanato so she must go with them. He tells her that unless she doesn't want a whipping, she shouldn't try anything reckless. Then while Ayato is drinking her blood, Reiji appears and calls him a disgrace. He tells him to be responsible and make sure she gets home, proceeding to leave and turning off the light.
All of them are seen eating at the dining table. Laito offers to Yui that he'll feed her, but Reiji scolds him by saying it's bad manners to get on his feet during a meal. After Shu gets up and leaves, Reiji complains how he's a deadbeat and nothing good could come from anyone who grows up spoiled. He then says that Shu won't even make an effort to attend their monthly dinner party. After that, he tells the rest that will be it for today, who get up and leave. When Yui gets up, he stops her and tells her that her table manners are deplorable and that one day he'll pull her aside and discipline her. Then when Ayato, Shu, Laito, and Yui are in the game room, he appears and asks them the meaning of all this commotion. Shu states that he couldn't care less about Yui, so they should be quiet and allow him to sleep. Reiji comments how he thought he would say something of the sort and how he shrinks away from any challenge, saying that he can't do anything without help then angrily calls him a deadbeat.
Yui spots Reiji sleeping. He opens his eyes once she places her hand on his shoulder and asks her what she's doing here. He comments how he can't believe he was woken up by the smell of her blood. He asks her what she's doing there and she tells him she came because she heard him moaning. He gets up and puts on his glasses, telling her to wait a moment and that he'll make tea. Yui stands there as he drinks his tea. He asks her if she honestly thought he would make tea for her and tells her to stop being so conceited. Yui then asks him if anyone else uses his laboratory, like maybe Shu. Reiji angrily states that just hearing that name makes his ears feel unclean. He then stares out the window, having a flashback of when he was younger. His younger self was staring outside at Shu and his mother. The flashback then ends and he tells Yui he'll make an exception and share his tea with her. Yui thanks him and drinks the tea before dropping it and covering her mouth. He tells her not to worry and that it won't endanger her life. He then opens her mouth and makes her drink something else. Yui falls to the floor, coughing. He scolds her how it's impolite to cough so openly then asks her what's wrong with her and how things that have been broken must be cleaned up immediately. Yui stares at her bleeding hand and Reiji grabs her wrist, then he says for her not to get the wrong impression and that he has no interest in things with imperfections but she infuses the air with a sweet aroma. He then licks her hand and asks what is this in shock. He stands up and pulls off his glove and tells her he's soiled himself in her blood. He orders her to stand on her feet before dropping the glove and pushing her back against the bookcase. He then proceeds to bite her and drink her blood.