Kirby
By this point, Nintendo is no stranger to the Musou games, with both Zelda and Fire Emblem being adapted by Koei Tecmo and Omega Force. There’s plenty of other Nintendo franchises that could use the Warriors formula as well, and none may be better fitted than Kirby.
With a host of cute characters and tons of different abilities, a Kirby Warriors game would definitely be unique. Kirby himself would be a big focus of the title, and his copy ability would allow for an incredibly unique warriors experience. You could suck up everything from Wheelies to Sword Knights, and use their powers to cut through hordes of Dreamland inspired enemies. The setting would also be perfect, as each Kirby game usually introduces some new threat trying to take over the various planets in Kirby, easily allowing for an original Musou storyline.
Besides Kirby himself, you have a handful of other characters that could be playable like Meta Knight, Waddle Dee, King Dedede, and Ado.