Need to pick a class that fits this idea

So, I'm making a story for this character and i have trouble looking at what it can be mechanically.

But the context of the character is:

She is an Oni that carries a flute, a Katana (or a Nodachi, have not decided more on this) that is a "Song of Challenge".

The way she fights is a bit different than her comrades, while others rely solely on Martial Arts and single weapons, she is very flexible with her sword and martial arts which she called Sun and Moon Style

What would this be?