Wow, this is impressive! I'm always impressed to see GGC-submissions tackling making something fully 3D, but this team managed to drive it home.
First impression of the game was great. Beautiful, engaging main menu with good support in settings, and you also did a great job with the easy-to-understand tutorial in the first few steps of the game. I very much enjoyed the look and feel of most everything, the world feels desolate, vast and bittersweet. You guys have studied your Ghibli for sure.
I also liked the aesthetic choice of letting the organic piano music take center stage. The way the single notes closely accompanied and waited for my progress in the first puzzle, only for the music to take of on its own whimsical journey as the puzzle completed and the game opened up was beautiful. Great, simple, way of letting the world tell the story itself.
Once I got into the bigger area with multiple paths and several closed drawbridges I felt a bit overwhelming and lost. While this might be somewhat intentional and even fitting for this type of game, consider studying your world and its topography to better decide on how you want to lead players around it. Right now it feels just a tad bit to open for me to make comfortable progress.
All in all it looks, sounds and feels great. For the few weeks of this project, it's impressive to see what you were able to get together, and with this amount of polish that you had time to get in there as well. I'm sure there is a bigger story to this world to be told if you had the time, but even so you managed to give the core of it all a chance to plant its seed.
Very well done. Congratulations!