From what I've gathered, the plants have a sort of copycat ability to sap the abilities or arts that other people here might have. It's likely one of our fellow residents has some sort of hallucinogenic ability.

[ She wouldn't be surprised to hear it's Mizuki's, of course, but she isn't certain, so she's not going to just throw out accusations. ]

If you're unfortunate to end up out here again, it seems to be vision-induced, so just don't look at them directly.