Awesome game! I'm super amazed that you were able to do this in RPG Maker!
[MAJOR SPOILERS BELOW]
Funnily enough by the time I got to playing, I forgot it was part of a Yandere Game Jam and was totally shocked by the twist! I had my theories that either Siren was evil or the dark stuff was accidentally made by Nao somehow, but I wasn't prepared for the actual ending! It was amazing! I really hope for a sequel where Siren is able to escape, maybe.
Hope to see more great games like this!