Hello, very fun game! Took me about 5 tries to beat it on normal mode, then I tried a couple times on Sadistic to see what it was like, but wasn't able to win. In general I think the gameplay is enjoyable, and not too difficult to get the hang of, especially since most of the attacks are pretty well telegraphed. It might be more of a problem if you plan to have bullets that come from all sides of you, but for what you have here, it was easy to get the hang of.
I think the inclusion of then local culture didn't take anything away from the game, and seeing what you had to say about them in the game page made me more invested. I think adding some of the stuff you said on the game page on the fun fact screen in-game would have been nice too, since I didn't make the connections from the pictures until after I reread the page. Also I can click the images, but I don't think they did anything when I did.
For the learning curve, it may have been just me, but I struggled the most during the whirlpool section, I think the distance made it harder for me to tell if I was hitting the target. Compared to that, the final section was a bit easier for me.
Edited to add: Also I would have appreciated a tool tip about using the shield. I saw the controls for it in the options, but when I started playing I completely forgot I had that option. You may not want them to be forced to use it during the tutorial part though, so maybe a quick reminder before the proper fight starts would help.
I also wanted to say that I liked the ascending tones counting how many jumps you've used, and having Song make her noise once you're out of jumps.