Nero Chaos

This vampire is known as the tenth of the twenty-seven Ancestors of Dead Apostles, as well as the highest ranking vampire to appear in Tsukihime. Has 666 beasts on his body, from deer and wolves to mythological creatures like unicorns.

Spoiler

The only conventional way to kill him is to destroy all 666 beasts at once or he will constantly regenerate; to kill him is practically impossible.