Ooh...you did an excellent job integrating the RM2K menus and battle system into a NES-like game. If it weren't for the Enterbrain logo and some RTP sounds (pure mid-2000s nostalgia for me!), I probably wouldn't even have noticed it.
The graphics seem really authentic to me. The colors, the dithering, the UI...I could definitely see this as an actual game from that era. The characters, enemies and story so far are also pretty old school.
I had to read the comments on the game page to see that the current version pretty much ends after finding the mirror, which was a bit frustrating after searching the whole map. I think that should be stated in the game, especially if it's only a demo.
But other than that, this is a really impressive little RPG!