I found this game a bit late, and I'm not sure if you have plans to develop it any further. But jsyk, every time I've played it (in-browser each time so far) I've had the knight automatically corrupt at the end of the first round, with no text explaining anything. I tried intentionally letting her die during the first round to see if anything different happened, but after multiple textboxes she ended up just leaving for good.
Some smaller notes:
-I find it really fun overall! I've played quite a few games of it today and will probably do a few more tomorrow (still haven't gotten to fight the final boss, although I did get the fully corrupted ending)
-the big exception to it being fun is that it can be a bit grueling at times especially early on with the enemies that add x4 shields to themselves. since it stacks it can easily get to like 16 or more for me which can get frustrating when you don't have much options for damage yet
-"heal all" doesn't seem to work for me? it just seems to be acting as a regular +1 heart
-the art style is so cute c: