Can /tg/ help me come up with some plot hooks/ideas for creatures for a game, in return for pictures.

Friend of mine is running a Japanese mythology orientated dark fantasy game, the basic setting is a sort of paralell of Edo Japan with monsters known as spirits, some of which feed on humans, PCs are Spirit hunters, a sort of half-mercenary, half-Ronin, half-government funded racists murderers organization that hunt down and deal with spirits that are causing problems/eating people.
The problem is, coming up with ideas for Spirits, coming up with ideas for slightly grittier encounters (Game has a whole Noir feel going on at times, in that while not grimderp, it can be quite grey on grey and even the main characters can be right bastards.)

I'm looking for ideas for creatures, based on Japanese mythology prefferably, ideas on various hunting methods beyond 'stick the fucker with a sword' and ideas for more normal encounters, such as crooked nobles, deserters from the army, benevolent spirits hiding from lynch mobs, ancient sealed creatures, ect that we could use, as well as maybe some advice on how to make the setting gritty and dark without going over the top.

Any ideas?