Thank you for playing and for your detailed comment!
I'm glad to see that the aqua boss works well, the whole sequence is very inspired from the SA-X in metroid fusion.
The upcoming release will change a lot of things in terms of weapon balance and enemy life, I hope it will solve some of those frustrating moments. Also, sliding will allow you to avoid enemies which completely changes the pace of fights (Ayame's fight in particular)
The ice shield is still in the game, you were not far from unlocking it I think! Certain abilities are needed later to unlock specific parts of the game/beat specific bosses so even if they are very situational most of them are still used at some point