Awesome so what was really wrong with Patchy is that she was part vampire the entire time.

Patchy onee-sama I like the sound of that

Or maybe, she just has have her low blood pressure refilled...

New cure for anemia.

So Patchouli seems to make a better vampire than Remilia... Looks like the mansion has a new mistress.

Actually, as far as I know, Patchy is a youkai... and as far as I know, youkai like humans as their desserts... makes sense, if that's human blood...

Actually, given that she originally asked for WATER, and was mistakenly given that jug of BLOOD instead, it seems obvious that she was just choking on some errant chunk of half-chewed food.