Strong entry, and i really enjoyed the upgrades system where there's not just more hp but also movement upgrades and additional spawning items you can unlock like the shades.
The artstyle is beautiful both the 3D gameplay segments and the illustrations on the menus you've nailed the japanese style here, and that music loop completes the package . Also have to point out that it's really clever to have used the whole Koi becomes dragon myth fot the evolution theme ^^
If i had to nitpick i only encountered 2 small issues, sometimes once you've dodged an obstacle the time your animation gets back to idle your tail can still hit things and damage you after you passed it, and a tiny bit more visibility for what's ahead could be nice.
Other than these, it's all good, the game is fun, and i like that considering the theme you based it on you didn't made it endless and have the actual goal of reaching the top of the stream, plus i really liked the little detail of the map showing you how far you went each attempt.
Good job and well done :)