Those are themselves the vampire Alucard. Blood is how souls are bought. A currency of life. It is just the intermediary to trade and sell a life. To suck blood is to take all of someone’s life for your own. You understand that now, Seras Victoria.
Integral Fairbrook Wingates Hellsing / インテグラル・ファルブルケ・ウィンゲーツ・ヘルシング“I’m surrounded by idiots.”Hellsing (manga & anime)