Sora no Otoshimono: Tokeijikake no Angeloid

Exactly the same formula is placed in the titles - a mysterious girls and expanding dead premise which is still dead. Overall, they mean nothing for plot, but if you want to get a synopsis before the next season, take "Sora no Otoshimono". Or if you want to see so poor fanservice, cuz you have just watched the second season, choose "Date a live".  

The main characters of these animes are so much alike it's amazing. Both share the same amount of pervertedness, same morals, same almost everything. They also have the harem thing going on even though in Inukami it takes a little bit more time to progress. Both anime have that side character loves the main one but the main really doesn't care so they get the shit beat out of them thing going on, which is fun to watch. I highly recommend this if you like Sora No Otoshimono.