a Fudakaeshi is a malevolent ghost similar to an Onryo that exists to try and remove Fuda, a protective charm found in Japan that stops evil spirits and yokai from entering a building.
Since Fudakaeshi are themselves a type of evil spirit they must have humans remove these charms for them and will resort to seductive, intimidation or trickery to do so.
Once they are allowed in these spirits almost always cause misfortune or death to those foolish enough to have fallen for their trap.