Excellent work there. The only main crit I can say is that Mercury's side felt dominating compared to Jupiter's.
As for the name...yeah, that's a tricky one. Like I've watched through Ultraman Orb, where his powers come from combining the powers of two Ultra Warriors, and the form names are based on the two's special attacks. Ultraman Geed does the same thing, but the names seem more "generic" for a lack of a better word. (Of course, there's the DBZ side of things.) I think one of the earlier comments had a good idea.
Keep it up, and I hope to see other fusions as well.