Henshoku Kyuuketsuki wa Oazuke-chuu - Vol. 1 Ch. 4

[MangaDex]

 

[GreenDude1]

My opinion has always been that any vampire that doesn't have to kill to get their fill and just chooses to kill anyways is a moron. The average person has around 5 L of blood, you can lose around a liter of blood before it starts getting into the territory where death is a possibility. Blood comes back. If you took a full liter of blood it would take a couple weeks for it to replenish but it will replenish. 100 people could easily give you 100 ml of blood a day and regenerate it in less than a week. Just like that you have infinite blood supply without ever having to worry about it running out.