i love one piece, but you have a point XDThe thing about One Piece is that we already have Nami and Robin, and no other female character in the series is as significant as those two. But it's possible.
I don't know if they will be within the "mainstream" category, but the "Fate" series has a lot of characters and a recent collaboration with Honkai: Star Rail, there is also the slime anime "Tensei shitara Slime Datta Ken/That Time I Got Reincarnated as a Slime", or "Shokugeki no soma/Shokugeki no Sōma/food wars", again, I don't know if it is the category you are looking for or if it is the most mainstream, but taking advantage of the fact that this is a forum I suppose that someone else will say if it is or not XD