"Grind" was real for this one thats for sure!
Last two areas definitely took a while to get through, when trying to play properly, but once you get all the pickaxe upgrades you can just dig straight down to the boss, so that kinda balances it out a little bit.
There should have been some kind of indicator after fighting the boss though - I won, and tried to jump over them, but the speed boost from the jetpack launched me up and I died to fall damage, so I dug all the way back down in case there was something in the arena I needed, just to fight him again and realize there was nothing else, so I had to teleport back and come to terms with the fact that I wasted close to 10 minutes or so.
I also noticed that you could interact with the stores without them being found - I was able to buy from Shiori and AutoFister shops without having found them yet by standing and clicking in their area. Didn't check with Koyori, but I would figure its possible. Also after unlocking her (Koyori) Cece and Gigi just kinda showed up, not sure if I managed to sequence break there, or it was intentional.
But there's a lot of content here, which is impressive, and the art, music, SFX, and general vibes are all really nice. Great job putting this together!