Great art (MC's model is great, would love to see her in a more action/adventure/rpg game . I'd love to know the artist's influences; I mostly saw a megaman inspiration, but am sure there is more in their heart), great voice acting (elder tree and MC are very well acted, Bikerman is good, Tortoise I was going to say wasn't very good, but on second thought, I think she just didn't have a very good script)
The game controls terribly, but rather than unplayable, I think it is a charming terrible. A unique terrible. Taking control of it and learning to work it out is very fun. Which is why the second and third boss were quite disappointing, it's like you didn't want to make me continue fighting with the control mechanics. Not in a mean-spirited way, the first boss was pretty simple, but making me engage with this chaotic platforming made it a special gameplay experience, and I'd love to see more of fights like the first boss. (The second and third boss didn't even feel like I was fighting them either, so I can't say it was very fun, since neither the controls or the bosses were challenging me.)
It'd have been great to have to dig my way through the boss and find their heart to hit, I think that should be the gameplay you look for in this game. Dig through platforms for the weakpoint, or dig into the boss to find the heart, both of these require mastery of the very difficult controls. I beg you not to give up on this concept, because I loved the challenge imposed by it, but do refine the enemy/stage design to put the digging on the center stage. Call it Shadrill of the Colossus the way I want to dig for where to hit.
I liked the second stage's BGM the most, very good composition.