Hemonomic Principle

Idea Blood. It is a quality of the blood that makes Ancestors deserving of being Ancestors, and a basic precept carved in their soul. A singularity that rewrites the physical laws of the planet just by making blood circulate.
A Dead Apostle who inherited this blood would be promoted to Ancestor no matter their rank, and Arcueid compares it to a “royal crown.”
On the other hand, a millennium-class basis is required in order to make the Hemonomic Principle work, and a Dead Apostle who has been around for a few hundred years would be crushed by that Curse even if they have inherited it. That’s how it used to be, but thanks to the ritual conducted by a certain Dead Apostle and his thirst for revenge against his opponent, his sanity remained until the very end.

Tsukihime Material I: Tsukihime Work Glossary