Audience-Alienating Premise: The premise can be this for some people, since it involves young-looking Moe girls designed to appeal heavily to the Big Brother Instinct and May and Mayfly December Romances are rampant (no one that has an implied relationship with anyone else looks near the age of their partner). Most of the girls attracted to Kouhei don't look his age, particularly Hazuki and Kaoru. Kouhei's grandfather doesn't even get away from this, as there's an implied relationship between him and the vampire Elfriede, who looks like a 20-something year old woman.
Complete Monster: Count Heinrich von Kinkel was always a nasty customer, with his habit of sadistically tormenting and trying to murder the majority of the cast. As one of the eldest vampires around, Kinkel believes anything around him is a toy for his amusement or enemy to be destroyed without mercy. It's revealed in flashbacks of his fledgling Elfriede that Kinkel seduced a human woman, drove her insane and returned many years later when the daughter was a teenager. Kinkel turned Elfriede into a vampire before slaughtering the human family who raised her. He then forced her to drink the blood of her best friend, gloating how Elfriede was his slave. When Elfriede was done, Kinkle proceeded to gloat that her pain gave him joy to no end. I Hate You, Vampire Dad doesn't begin to cover it.
Ear Worm: The opening theme, "Neko Mimi Mode" (more like "Neko Mimi Modo", seems to be specifically designed for this, with lines like "Neko mimi / Neko mimi modo / Neko mimi modo desu".