Mizu is being infested with a demon and the only way to keep it at bay is to make her happiness 100. To increase her happiness you have to play her songs. If you play songs she likes you'll see her happy and her happiness will go up. But if you play songs she doesn't like she will become upset and her happiness will go down. Each time she becomes upset the demon will become more visible and get closer. If it gets too close it will corrupt Mizu and you will lose.
Yes this is similar to my Mizus Music Box project. I made that project and got inspired to make this game. This is just a demo i wanted to see what people think about it before i continued