I liked the shifting physics of the different levels (specifically the ocean and galaxy ones), making the same battle feel a bit different each time. The writing was also pretty good.
I would have liked some better hitboxes on both the shadow and the player; a bunch of times it felt like I got hit without actually hitting anything. Also, if I didn't have to go through the text every time I restarted, that would have been a smoother experience.
Overall, a decent game, though it could have used some more mechanics to add some variety in terms of strategy; my method for each battle was basically the same every time. If the shadow moved in different patterns with each level, that might have been nice?