Extremely promising game and amazingly executed too, good vibes, pleasing visual direction and the gameplay feels nice and responsive.
I found a bug that sometimes the game is sometimes stuck after the "Get Ready, Start" text until you pause and resume the game, maybe there are some other ways. It also makes the camera not zoom towards the player while the text is appearing, instead the entire girl is visible the entire time and the zoom only starts once the game gets unstuck.
This is extremely annoying in browser in full screen mode because pressing Esc turns off full screen before actually sending the keystroke to the game, forcing you to restart the game if you want to play in full screen because you can't turn the full screen of the game back on without exiting the level, and that means getting stuck on "Get Ready, Start" again once you are back.
Not sure what causes it but I believe it doesn't happen when opening the level first time after opening the game (even if the game loads a save) so the cause of it might be related to something that happens when/after playing a level but gets reset whenever the game is restarted and changes to the save file don't seem to affect it.
Aside from that, it's probably worth fixing the body proportions of the tutorial character, her torso feels way too long compared to the rest of her body out of other things. I'm assuming it'll be quite a lot of work to rework all the animations and hitboxes for the clothes, but still I think it's really worthwhile. Since the game is largely focused on the visual aspect it's good not to make a bad first impression for an average player by making the 1st character look uncanny. I'd highly recommend googling something along the lines of "anime character proportions reference" and rework the artwork a bit based off of the results you can find there. And while at it I'd strongly recommend (possibly significantly) increasing the max breast size, tho that's just my personal flavor of horny speaking, which should probably be ignored for the good of humanity.
Final thing I'd like to point out is the fact that bullets seem to stop existing as soon as they reach the two status bars at the top of the screen, making you unable to hit enemies that you can still see on the screen above and around them. It's rarely a big hurdle but I found that it really throws me off whenever it causes problems, whether it's me misjudging how much time I had left to kill the given enemy or assuming I can dodge above one, only to find the spaceship unable to go into the area that *feels* like it should be accessible but in reality isn't. I'd probably suggest making it clearer where the game area ends where the bars area starts by making the invisible wall visible, or extending the playable to the entire screen area and making the bars partially transparent, but in the end I think that would increase the visual clutter which can get relatively strong at times, so the best choice would be to make the unplayable area completely opaque and/or moving the bars to the bottom of the screen so that they don't distract the player as he focuses on the gameplay in the upper parts of the screen, since the information they contain isn't crucial at all times, unlike enemy positions and similar.
Above suggestions aside, I wanted to mention that I really applaud the current balance of difficulty: It's right in the sweet spot where after a few tries you can reliably perfect the level, while still being difficult enough that doing so makes you feel the satisfaction from pulling off something challenging. Combining difficulty with completionism adds a lot of replay value, as opposed to for example adding a toggle somewhere that decreases the enemy count or whatever.
All in all, I enjoyed this demo a lot and I'm definitely looking forward to what this project will become in future!