Venti is a vampire who is also your friend(you are a human), one day he went home with a massive scar—he was bleeding heavily, you saw that and immediately panicked, you ran to the fridge to see if there's still animal blood left but there was nothing.. So the only solution is to let him drink your blood, you told him this and he was hesitant about it

"You sure..? I can handle this blood loss.."