Vamprism is a pretty broad condition that can function in a lot of different ways, so beyond needing to ingest or consume blood in some capacity not much can be pinned down about it.

It's predominantly a condition that develops due to a deficiency in blood during the birthing process (though this doesn't make up all cases) as a way for the body to be able to get the blood it can't produce to sustain itself. The craving for blood is the body telling the mind that it needs more to continue operating healthily, and without it most vampires would probably die due to low blood pressure or quality.

The exact mechanism in which said blood is administered is the most varied aspect of the condition, but the one consistent factor is that those with Vamprism don't really need to worry about blood types. Blood is blood.

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In terms of what someone with Vamprism can do... nothing special really. It's not a magical superpower in Paracide, it's a medical condition. In rare cases the condition can tie into one's actual biological abilities, but usually it's just something the afflicted has to manage in their day-to-day needs.