I've seen 'fusion' and 'crossover' used both interchangeably and to mean the other's meaning depending on who's saying it. It's kind of like the 'gen' rating and 'dubcon' in that no one seems to really have a definitive definition. :p

So far the fusion's working! And there are a lot of characters to play with. XD It's very T&B heavy so far, but that works and makes the CG bits more mysterious~

I dunno. Crossovers (the hypernym) are fun! This might be habit forming. ;)