Hey! Thanks for playing the game! I'm glad that you liked it. I watched your video and first thing first, yes, there is a way to finish the demo peacefully! The key to do that is the poem on the stele. When you have talked about the lock and the key to the statue, whether you insisted or not, negotiations are now available. Try talking about the works of art again and some new text will appear.
About the character speaking, it definitely is something difficult to talk about without spoiling the whole plot. If her name does not appear you can consider it more like omniscient narration. And if her name appears it's something that she definitely wants to say aloud and not think.
When I made this game, I took a lot of inspiration from Umineko no naku koro ni , which is another visual novel. And one of it's particularities is that what you see is not always what it seems and the player kinda has to make its own opinion about what is real or not.
My two other inspirations to make the stories were the original "little mermaid" tale, where souls are kinda an important plot point, and the Fiji mermaid, which I won't elaborate on because it is a very big clue to understand some of the story aspects, it's a real event that happened and you can google it pretty easily if you are interested to know what is it about.
For now, I don't plan to release a full version of the game. I worked on this demo for a year and right now, I want to experiment and try writing new stories. But this project is still very close to my heart and I still plan to expand it.
Again, thanks for playing!