Played for like 30 minutes, got as far as the Oni showing up (for reference on what i've seen). Right off the bat, I like this game a lot. for constructive criticism:
Rebindable controls are highly recommended. Having dash be on a trigger i feel would be way better, so i don't have to lift my thumb from attack to move around. Azumi's dash doesn't feel that important, as only the Oni enemy seems to benefit from having advanced movement, because the level certainly doesnt do anything for it.
The shuriken using meter i feel is a good choice, but the balancing for cost or regen is off I feel. I get too much meter too fast, and theres no meter management happening in my head at all, no reasons to consider my actions more thoughtfully.
I think the oni needs more wind-up for his attack, so the player has more of a chance to react to the swing, as it is currently, I dont think i have enough time without dash spamming.
For the love of god, change how zoomed in the camera is. I died plenty of times dropping from one level to the one below and a slime hurt me. What I'm landing on shouldn't be a question of am I going to get hurt or not, The player should have that information easily available to them. As i'm sure you know, losing in an action game should be the cause of the player not acting well enough to something, not by something they didnt see from out of nowhere.
Azumi 's dash should be straight, no arc to it going up or down. The player should know what their dash will be every time. If you want to add diagonals and have the dash be arched slightly thats one thing, but the aerial dash should be consistent.
I agree with what Nate said on a podcast, Azumi feels slippery. the jump doesnt feel exact enough, like theres too much input lag, probably an engine thing or because its on a browser, but I feel it is an issue.
Keep it up Tom, cant wait to see more!