Not too shabby of a little game! The concept is a decent reversal and makes for some fun fast-paced gameplay, and overall the game has a decent amount of polish and nice special effects to make it exciting. Had a good little time with it.
In terms of feedback:
The whole mechanic of nullifying enemies blue which opens them up for a glory kill felt a little unnecessary in its current state. Yes, it is satisfying to finish them off in such a manner, but because they aren't able to recover from their nullified state over time, there is no reason or incentive to finish them off quickly, making the sword slashing feel like just a victory lap: at a functional level, they're already dead and the enemies may as well just self-destruct immediately without needing to be slashed. If they did recover over time, however, that might've added some more interesting combat where you need to split priorities.
The difficulty curve is a bit out of whack in both directions: it takes several levels way too long at the start of the game to get to an acceptable level of challenge which makes restarts painful, and then near the end it gets way too hard that it was as well be impossible (unless I'm missing something). Got extremes on both ends!
The decision to make the boundaries where missed bullets will hurt the player not match the bounadries of the player's walkable area creates an annoying, hopeless situation where when a bullet passes the walkable area, all you can do is watch the bullet fly, unable to stop it until you take damage or die. Hurts way worse to have that moment of hopelessness with no recovery rather than just taking damage immediately. Maybe the area between the two boundaries should be walkable and have the bullets turn red as a warning, or maybe even slow down, to make recovery possible and create more excitement.