I never seen this in a demon slayer game (that I can recall of anyway) and it would create more variety between players and allow differentiation. Add katana customization, this could be mixing and matching different hilts, handles, and guards. There could also be minor accessories like chains, effects, and patterns on the actual sword.
This does NOT have to be major and doesn't have to be this HUGE selection (unless that's what you want as the developers) but make it so every katana does not look exactly the same. It would just add some variety and more customization options.
You could buy these accessories/patterns etc. with yen OR they could be boss drops IF you plan to have that.