How do you imagine a combination between these two going? I'm pretty familiar with RWBY and I've played Monster Hunter: World at least. There are similarities between the two, with the giant transforming weapons and the big monsters, but in a lot of other ways their pretty different; particularly in tone.

In RWBY, humanity has been corralled into a small number of defensible locations by an endless time of soulless creatures whose sole purpose is to kill humans and destroy their creations; the Grimm are drawn to negative emotions and people are terrified of them.

In Monster Hunter, humanity is thriving. The monsters aren't monsters at all, they are just large animals which people gleefully study, hunt and then make hats out of. There are a few that are more intimidating, but even something like an Elder Dragon isn't really treated as a major threat beyond "Hmm, might disrupt the local ecosystem. Better go kill it". I haven't finished Iceborne yet though; maybe the really end game stuff is different.

Basically, what kind of world do you want to make from these two? Which elements are you planning on borrowing and which side does it lean more towards?