Ran into a weird hard vore manga called Saiteihen no otoko (translation: Scumbag Loser). http://mangasee.co/manga/?series=SaiteihenNoOtoko
A lot of the early vore is off panel but the vore you see on panel later seems to mostly be f/m.
The story is that one day the main character (fat loser guy who has a body odour fetish) makes up as story about having a girlfriend and shows his peers picture of a girl he used to know. Later the girl somehow transfers to his school and backs up his story. Obviously the protagonist is suspicious especially since he knows the girl actually died years ago.
Turns out the girl is actually a scary maneating monster/demon. She starts blackmailing the protagonist into finding other 'scumbag losers' for her to eat. Whenever she eats someone she replaces them with some sort of clone monster. Each one of these 'monsters' has a really really creepy looking grin.
http://a5.mangasee.co/manga/?series=Sai ... =1&page=43
http://a5.mangasee.co/manga/?series=Sai ... =1&page=35
As I said most of the voring is off panel but at least the dialog is interesting enough. I think the manga is finished but the entire manga hasn't been translated/scanlated yet.
Spoilers - Links to some of the more vorish pages (WARNING: gore, disturbing imagery)
Spoiler: show
