Glass no Kamen (2005), Pretty Rhythm: Aurora Dream Recommendations
If you've seen one, you'll like the other. Although Pretty Rhythm is newer, they are very similar because both share the same ideas about severity in the entertainment world. I consider Pretty Rhythm to be the new generation Glass Mask (Aurora Dream exclusively).
The reason is because Pretty Rhythm's backstory is exactly the same as Glass Mask but left unfinished (I haven't finished Glass Mask but I assume it ended properly), and the main characters are left to close that story. The reason why I like Glass Mask was because the previous generation of idols in Pretty Rhythm in which they mirror the Glass Mask characters,