We can't always have what we want.
Eliana wants boys. Not in the way a normal, human teen would want them. Well, maybe that way too. But mostly because as a teen succubus she's starving.
As much as Eliana wants to deny it, she'll die if she doesn't feed soon. The solution sounds simple. Just eat, right? The problem is that boys taste too good, and Eliana's afraid the cost of her life will be someone's death.