The "Knife" effect, which can be used to kill NPCs, is found in the dark world.
Madotsuki can't wake herself up while she has one of the two effects active where she doesn't have arms.
The drinks you get from using your money you got from killing various NPCs gives you HP.
At the ending screen, two jellyfish appear onscreen. This may make no sense whatsoever, until you get into a theory that says that the whole game was a dream. Madotsuki simply woke up by jumping off the balcony.