Okay, so I'm writing a story, and my (female) character calls my (male) character "vampire" (he is literally a vampire, it's not a figurative use) as a term of endearment. It's inserted into an English sentence (she says, "I know, [correct form of the word "vampire" in Czech].").
It seems like I should use upír + diminutive? But I don't speak Czech, so I have no idea if that's right or, indeed, how to form the diminutive. Any thoughts?