UHS Hints is really helpful.
To add this from Malcolm's walkthrough:
If you've collected all the artefacts of Na-Tiexu the globes above all the mirrors should be flashing. The artefacts are as follows:
Astrology World (Purple) - Star Dust
Spirit World (Green) - Grail With Spirit
Magical World (Pink) - Symbol Of The Magical World
Crystal World (Gold) - Bell
I haven't played this game in years, so my memory of the nuances is pretty non-existent.