MegaTen
You also have a demon with you that yuo convince to follow you. It will do anything you tell it to and you can even control it by just pressing "tab". You can then fusion two demons together to get a completely new one (and most likely alot better) acquiring skills from BOTH the previous ones.
There are promos almost all the time and events where you get to meet GMs daily and you can even meet them in Babel from time to time to chat with them. Really good game
Aeriagames commercial:
MegaTen link:
