From what I recall and googling for a guide....
There are 16 different endings in total. Each heroine also gets two endings, either you didn't drug and rape them which will bring you to their "pure love" route or you did drug them and rape them in there sleep which brings them to their "fallen" route.
Requirements to unlock the individual heroine endings are,
don't smash any other heroine other than your "target" heroine of the playthrough.
your heroine becomes the maid of the inn
defeat the 10th floor of the labyrinth with your army and the chosen heroine beside you.
There are also two harem endings and yes, one for "pure love" and one for "fallen". You need to make sure that you get all the heroines as maids and make sure if you're going for "pure love" don't drug and rape them in their sleep and "fallen" is just all the rape fest you want. Once all the heroines are your maids, clear the 10th floor of the labyrinth and what ever you decide to do with the heroines while they were in the inn will result in which harem ending you get.
There are also random events that happen around the inn now, either in the day or night.
While you are walking around the inn, if you have any heroines that are maids, they will either have sex with the inn keeper or the male patrons. This are all random and do not appear in the gallery, well not mine anyway.
That's all what I recall. Back to Nikke