I'm not a fan of SRPGs and I think I'm half way through this one. That says something. I'm probably doing the demon fusion thing wrong, but I basically heep fusing demons as soon as I gain a level rather than keep the ones I like. I'd rather see them all.
That is precisely what you are meant to do. For the love of god don't keep a demon that you like for too long, they quite quickly lose their edge. Fusing them into higher demons is always a good idea.