It sounded like Hau's battle music but different from the one in the demo we heard awhile back in the year, it reminded me of how the R/B/Y & FR/LG rival music changed as you progressed in the story. What if the same happens with Hau's as we battle against him as we get closer to the end game.

Now Hau may not be the serious rival people want, but what if as we battle him, his battle music changes as he becomes more determined to give you the great battle you deserve because you two have been through so much?