① Corpse Eating Demon
② When a vampire sucks blood, some vampire blood is left behind in the body of the victim, which prevents the body from completely dying despite being “killed.”
③ A few years after death the brain has completely rotted, but the soul remains affixed in the flesh.
④ Eats other corpses to restore its rotting body.
⑤ After completely restoring its body, the ghoul has matured to be a Living Dead.
⑥ About 1 in 100 people who have their blood sucked and die become ghouls.

Colorful MOON Tsukihime: Tsukihime Dictionary