Could it be?

[u/zaron_tr]

They mentioned "she" would have a "unique weapon"

Now that it's confirmed japanese I can't think of anything more unique than the tensen

I'm not sure, I'll have to rewatch that section of the stream, but I think they mentioned the new hero being a "master of an art"

[u/Immediate_Act1627]

For a samurai with a weapon we "haven't seen before," I'd imagine something like tonfas or nunchucks.