I liked the dialogue a lot too. The chemistry between Ao and Peperi, and of course the true protagonist Mr. Sol, really has some interesting places to go.
My feelings are pretty much the same as the other comments. It's a really fun demo with a neat base idea that lends itself to puzzles. I also liked how you threw in the liquid physics and the ball pit. Those were actually some of my favorite and most memorable parts, so despite their "danger" mentioned below, I'd probably argue in their favor.
There's just one thing I wanted to bring up since I haven't seen it mentioned before: From what I see, ranks are distributed based on completion time right now. However, when I stop to let the dialogue play out, the time also appears to keep running. Just moving on didn't feel right either, since I'd have to worry that the next event might override the current dialogue.
Bug-wise, I didn't really find anything. When doing a coin collecting run and collecting the final coin with Peperi, I can still make sounds when pressing the jump button, that's all I really managed to find.
So yeah, all in all, very good demo. A lot of love put into details, like the underwater bgm effect and the parallax when doing the big jump with Ao. Good stuff, I had a lot of fun!