Honestly, this comes heavily down to intent and I apologize how harsh this may seem if I am reading this wrongly, however:
If this game is attempting to be a rage game. It overall succeeded in that goal. If it isn't, I have some points of criticism. The main thing that changes this game's quality is whether these issues I have are intentional and I cant tell which, but am leaning on the side of this not being intending to be a rage game.
-First, the way of handling hakkeru movement with the mouse is really janky. You can put your mouse over the whole screen and the mouse does not move with your character nor screen transition. It feels like the game expects me to pull quick trick shot maneuvers with it while in reality it is a really imprecise feeling control scheme because of how long it takes to actually maneuvar, both in general and to keep up with the players current position. It, in its current form, is unfit to be used in a reactionary environment. If the intent wasnt making a game that felt as I walked away feeling, it may be best to either ditch the mouse aiming entirely in favor of using the arrow keys to shoot your shot, or limiting the mouse's position in game to a circle around the player that moves the mouse alongside the players movement, allowing both persistance of aiming angle in relation to the player while they are moving as well as allowing quick snappy mouse input without the jank that can occur when you have to move the mouse full screen to even start adjusting it in relation to your constantly moving player.
-Second, the hitbox on the player before they get hit/forced to reset is rather strict, there are times where it feels like the sprite on the player isnt even touching a boundary before it is marked as a death and it can be difficult to gauge where is safe to move and where isnt. I'd suggest making the hitbox for the player smaller than the sprite. There were also a few rather demanding spikes of difficulty throughout the game because of the above two mentioned issues.
-Last, screen transitions. You can still move during screen transitions and this has led to multiple deaths where I can not see my character until they have already walked off and died, during lucky times Id just be placed at the start of the new screen, at worst Id have to redo the existing screen. This by itself wouldnt suck so much if it wasnt possible to walk backwards into the previous screen (or instead of walking, being hakkeru blast from a mouse click I did a split second before my death into that previous screen) and then subsequently die, respawning on that previous screen, losing all progress for a whole screen. experienced this at least once on the last screen of the game where I had to redo the one before it. You can cut this issue by making the aiming changes I mentioned above as well as pausing game logic while a screen transition is occuring.
If you were making a rage game, thumbs up, goals met and the above issues are likely intended. If you werent, please take mind to the above. I am sorry for the sour response, hopefully I was able to be more constructive than not.