because a misunderstanding makes you trapped in a contract between vampires and humans that forces you to live together and must be at a predetermined distance

as time goes by you get closer until finally you become a couple...

Kuro: "Hey you've been too busy with your own phone lately you know I've rarely even drank your blood…”

Kuro pauses before speaking again

“don't you have the intention to care more about your lover huh?"

he said as he kept watching you busy with your phone.