This anime is ostensibly aimed at a female audience. It's technically a reverse harem, with a solo female protagonist in a house full of very sexualized male vampires. It's a gaggle of pretty boys doing bad, playfully sadistic things to this hapless female, over and over and over. There's some hinted at plot involving the girl being the adopted daughter of possibly a priest, and of her rumored to have been a tacit blood sacrifice by the church to keep the vampires and the forces of darkness at bay...all she knows is that she's supposed to be attending boarding school...but it's a night school...specifically an over-night school. Yes, the protagonist is made to live the nocturnal hours of a vampire, despite being a mere human. She's called the "Bride sacrifice" by some of the boys, and basically she exists to have her blood drained from her little by little by all of the vampiric brothers in the mansion where she lives. Each is cruel to her in turn taking her blood by force on a whim, each seemingly no better than the other until the one tsundere pink haired vampire counsels her to make her escape during a crescent moon, which she disregards because she's still driven to solve the mystery behind her adoptive father and how he's tied to all of this.
Honestly, it's just not a very good show. It was mildly entertaining, but I have no desire to watch any of it further. It's just one relentless episode after another of soft core torture porn. It's really not my thing. The over arching plot seems like mere afterthought to the pretty/sexy boy vampire fanservice all over the place. I can see this appealing maybe to people who fetishize vampires and vampire fan culture, and it's certainly better than Twilight, but...that's damning with faint praise.
My recommendation is to give Diabolik Lovers a pass. The dub is adequate, the cast is great, but the story is just so "meh".