My Vampire Family Raised Me for My Blood

Synopsis

It was only after every drop of blood had been drained from my body, and my soul had already fallen into hell, that I finally understood the truth. My parents had never loved my sister more than me. They had simply been raising me like livestock. For years, they sliced open my veins to harvest my rare "Holy O-Type Blood," using it to sustain my chronically sick younger sister so she could one day marry a pureblood vampire Grand Duke. I time travelled back to the very day the blood pact was meant to be sealed. My sister once again pressed a hand to her chest, feigning weakness. My mother's voice was as cold as ever. "Cut your wrist. Feed your sister your blood." I let out a quiet laugh and took a step back, lifting the Holy Court's blood-testing crystal from the table. I said coolly, "Why so impatient, Mother? Sacred blood cannot tolerate even the slightest impurity. Before the Grand Duke arrives, shouldn't my sister prove her bloodline first?"