Might be an unpopular opinion but im personally not a big fan of crossover or "in-universe crossover" games with a story. There seems to be a trope when it comes down to crossover games, there are 2 or 3 adversaries fighting each other and characters from other universe are getting involved and recruited just to for them to ally at the end and to fight that bad guy who manipulated them in the background or something like that. Especially looking back at other crossover projects from Koei Tecmo it seems to be the case for most of them. I'm also worried that characters might act unnatural. Although one could argue that, after drastic changes where universes are merging together and monsters threatening to destory the whole world, that adepting and changing does seem rather logical. I actually would love to see something you suggested expanding the Story in its own realm and focusing on the playable characters from 3h and making them all available. One thing that would worry me though is that it might be unnapealing for 3h's fans going from tactical roleplay to hack n slash just to keep up with the story that got expanded.