Lapistia

First and foremost, regarding all the bloody (or should I say, sanguine?) quirks: despite the fact that Nihs possess this particular trait, they don't typically engage in such extravagant displays of bloodletting (for the same reason that directly drinking blood from a victim is considered unacceptable). Secondly, if a Heroes character possesses an ability similar to the one proposed earlier, it would imply that they have conducted experiments on themselves, which, for two reasons, would immediately classify them as a defective Nih.

How much blood is needed for initiation?

A few drops are sufficient.

Can it be mixed into a barrel of wine without losing its effect?

Well, IN THEORY, it might be possible.

That way, a Hero could pull off some impressive diversions: sneak into a fortress

And buff the enemies.