Cool game !
I really liked how you used the arena as a tutorial. The slow-mo was a really cool mechanic and fun to use. My only problem was with the hitbox being inconsistent with the visual, was a bit hard to tell if I was hitting or not since the only feedback was a lost of HP in the health bar (wich was a cool addition btw), would have been nice to have a different sound effect from when you miss and when you hit. The final battle was pretty cool too and the key was a nice way of including the lore.
Cool game, I enjoyed it.