As a medium and the starting point of magecraft, blood was the most important ingredient in magecraft. It would have been unthinkable for a magus to casually let out his blood in his territory with no intent to cast a spell. Of course, it would be a different matter entirely if it happened to be the magus’s particular habit. However, according to Kiritsugu’s previous investigations, the man Tōsaka Tokiomi was not so careless.

- Fate/Zero: Act 14, Part 4