Really impressively slick. Love the art style, animations, sound, music, story. Overall excellent package. Since you went to the trouble of adding a nice 'previously on' sequence, I think more one thing you might want to look into is explaining the sword's magic power mechanic a bit more for players who didn't play the previous games. I had a lot of trouble realizing what I was supposed to do with the sword. I also seemed to get stuck, so that the sword could only collect two elements in the cave and I wasn't able to progress. (Though maybe that's just me being dumb haha)
I actually livestreamed my playthrough, so you can see for yourself if it's a bug or if I just missed something. There's a timestamp for your game in the video description. Hope the video can be useful!