Getting exhausted from the party is putting the cart before the horse.

If you say there's an incident, let's resolve it, ze!

So, who's the perpetrator?

She's really nearby. That's because she's a participant of the party, see...

In truth, she's an oni.

But they're not supposed to exist in Gensokyo anymore...

Oni, hmm...... Ah!

...Vampires... The kanji used in the word vampire literally mean "blood sucking oni."