The Diabolik Lovers OVA is a special episode which was released alongside with the Diabolik Lovers DARK FATE game on February 26th, 2015. The OVA includes the Mukami brothers as well as the Sakamaki brothers and is supposedly an introduction to the anime's second season which has been green-lit.
The show opens with a full moon night outside the Sakamaki mansion. The first one to appear is Yuma, the third son from the Mukami's who is in the garden of white and red roses tossing an apple up and down. He soon stops and shouts for Yui (addressing her as 'Sow'), but there is no answer. He mutters how annoying it is that he can't find her and wonders where she is until a voice tells him to be quiet. He turns around and spots Shu, who tells him that his voice is a nuisance while sitting on top of the steps from afar. Yuma demands to Shu (addressing him as 'Neet') to tell him where Yui is, but Shu replies that he doesn't know and tells him to be quiet again. Yuma lectures Shu that he should always keep an eye on his 'prey', but Shu bluntly responds by telling him to go ahead and continue searching for Yui and to hurry up and leave the mansion afterwards. He then says he's going back to sleep and Yuma scoffs that this was a waste of his time before hurling his apple at Shu, who catches it single-handedly. When Shu looks up, Yuma has disappeared and he stares blankly at the apple in his hand. Unbeknownst to Shu, Reiji has been watching him from his study and he suddenly perks up when he senses a presence. He sighs that the Mukami's have no manners by infiltrating their mansion and he foretells that something 'troublesome' is about to happen.
In the bathroom, Azusa, the youngest of the Mukami's is kneeling by the bathtub filled with water watching his blood from a cut in his arm spill out, until Kanato appears from behind and demands to know what he is doing. Azusa calmly replies that he was only talking to 'Justin' (referring to the 'cut' on his arm) and Kanato tells him that he can't just barge into other people's houses and do that. He calls him an eyesore and orders him to leave, but Azusa changes the topic by asking Kanato where Yui is. Kanato snaps and screams at Azusa to leave, but is interrupted when Laito appears in the bathroom and he comments on the 'unusual guest'. Azusa tells Laito that he is looking for Yui (now addressing her as 'Eve') and he asks him where she is. Kanato interjects by asking Azusa why he is in the bathroom when he is trying to find Yui and he is not obliged to tell him of her whereabouts even if he knew. Laito tells Kanato that it is alright, for he too is also looking for Yui and comments that she doesn't seem to be around, prompting Azusa to question himself of whether he will be able to become 'Adam' or not.
In the game room, Kou, the second son from the Mukami's scores a Triple 20 on the dart board and tells Subaru (who is also in the game room) that it's his turn, but Subaru scoffs and asks who said he was going to play with him. Kou explains that he only came here to see Yui (addressing her as 'M Neko-chan'), but he can't seem to find her. He encourages Subaru to have a go and when Subaru refuses again, Kou slyly asks him if he can't do anything without Yui around. This provokes Subaru who declares that she has nothing to do with this, while Kou tells him not to glare at him like that. He is then interrupted by Laito who suddenly appears and throws a dart towards his face, but Kou manages to move out of the way. The dart scores a bullseye on the dart board and Laito sighs that he missed. Kou turns around and accuses Laito of trying to damage his face, since he is an idol. Laito replies that no one has been able to find Yui and they are all irritated, but Kou says that he's not bothered by it prompting Subaru to call him annoying and leave. Kou sighs that he only wanted to have some fun while Laito glares at him silently from behind. As Kou twiddles the dart between his fingers, his artificial eye glows red and he says that the real fun is just getting started.In the main hall, Ruki, the eldest son and the leader of the Mukami's is standing at the bottom of the grand staircase and the scene changes to where Yui is. She slowly opens her eyes and is surprised to find herself outside. Having no recollection of her earlier movements, Yui looks around confused, then murmurs that she was supposed to be in her room. She goes back inside the mansion, and is greeted by Ruki who suddenly appears and blocks her path as the doors close behind her. He tells her he has been waiting for her (addressing her as 'Eve') and Yui asks him what he is doing here. Ruki says that she needs to be disciplined (now addressing her as 'Livestock') for having made her 'master' wait. He approaches her and grabs her hand while commenting that he had never expected that the 'special' person they had been looking for would be a 'blockhead'. He pulls Yui into his arms and informs her that he is going to see how 'special' her blood is, then pulls back her hair and sinks his fangs into her neck. Yui squints in pain and attempts to resist, only to be backed up against the door by Ruki who tells her not to defy him before biting her again in the same area.
Just as Yui is about to lose her consciousness, Ayato appears. She weakly murmurs his name and Ayato
comments that he had felt a bad presence, so he went to investigate. He shouts at Ruki to not touch his 'prey', then runs up and snatches Yui from him by pulling her into his arms. Amused by Ayato's possessiveness over Yui, Ruki smirks and taunts Ayato by asking him if he is really bothered by the fact that he is able to take her away from him. Ayato angrily declares that all of Yui's blood belongs to him and he will not hand her over to anyone, then drags her away. As Yui is being pulled, she briefly glances back at Ruki before proceeding with Ayato. After they are gone, the rest of the Mukami's join Ruki in the main hall. Kou comments on how it was unfair that Ruki was the first to drink her blood, followed by Yuma who says it doesn't really matter since they will be able to drink from her whenever, and Azusa says that he also wants to drink Yui's blood. Elsewhere, Ayato slams Yui against the window and orders her not to be anyone else's 'prey' but his. Yui attempts to explain the earlier incident with Ruki, but Ayato cuts her off by yelling that she belongs to him, then pulls down the right side of her shirt and kisses her skin.
He tells her that her face is asking for it and he'll give her plenty before sinking his fangs near her chest. He then tells Yui to only fall for his fangs forever before biting her again in the same area. While Ayato continues drinking her blood, Yui's vision slowly starts dimming and she loses her consciousness.
After the credits, the Tsukinami brothers are briefly shown. Shin asks his brother, Carla, if they should begin and the OVA ends with Carla replying 'indeed'. 
List of characters in order of appearance: