It took me a while to figure out what was going on, but the idea is certainly very unique! The controls were nice and responsive, and the huge hitboxes of the characters took some getting used to, but fortunately the game didn't make it too much of a problem. The graphics, while simple, did a decent job conveying a unique setting for each character, and the music was a blast!
Obviously I skipped the upgrades and played Vert in 1-hit mode like a real gamer, it was definitely a challenge but not too bad with a bit of respawn invincibility abuse. I did go back and played them the intended way after the full game, and I have to say letting the player completely skip those upgrades in the first place is definitely a decision. I would say it's definitely interesting that they can be either the hardest or the easiest journey depending on your choices, but I think a more obvious indication of "you're entering hardmode" would have helped.
(Plus, maybe add a big pit leading back down to the start from around halfway through, so that the player has an easy "out" if they decide they bit more than they could chew?)
Buster was always a nice change of pace compared to the other two when the game switched back to them, but I did feel like the gunplay was missing something. I think instead of the three alternative shots (that I never really used), some kind of an active shield/deflect ability would have been a good match for their more aggressive nature, as the enemy bullet patterns felt a bit cheap at times with how fast they come at you.
Alma was neat but I think they were my less favorite character of the three, they kinda lacked the immediate sense of identity of the other two, and the block puzzles were alright but felt a bit shoehorned in just to give them something different. The puzzle focus in itself is a good idea, but I think some other puzzle mechanic like hacking or gravity manipulation would have been more interesting.
Overall, I think the concept of three unique playstyles is great, but it just didn't go quite far enough. I think in an ideal world, the Vert journey would either go full Celeste with the platform and spike challenges, or full Terraria with the drill. And for Buster, I'd have loved to see it just go all-in on the gunplay and turn into a linear corridor shooter, maybe with a bullet-time effect whenever switching in and out of this particular character to help the player get back into the action. (Since as it stands, Buster's and Alma's areas overall have a fairly similar feel to them.)
More visual distinction between characters would have been nice as well, in particular I think Buster and Vert should have been shorter than Alma since they have to avoid damage, while Alma could keep the giant hitbox since they're the only one who never gets hit.
Of course, all this is a tall ask for a gamejam, but that's kinda something you have to keep in mind when you essentially decide to make 3 games in one!
Still, definitely one of my favorite implementations of the theme so far, I think switching between the three perspectives does a great job conveying the sense of distance and isolation. All in all, nice job!