Leon learned about the Astral Prism from the game.
He didn't dare to guarantee he could use it effectively, so he specifically consulted Salovis, who seemed to have some insights.
In summary, the Githyanki had a son who inherited her ability to block spiritual energy, named Orpheus. Because when he charged while riding a dragon, a brilliant comet-like glow would appear, he was also known as the Comet Prince.
After the disappearance of Gith, the famous Comet War broke out between Vilakis and Orpheus, resulting in Orpheus's defeat.
Vilakis declared outwardly that Orpheus was dead, but in fact, she secretly imprisoned Orpheus in a special cage, which is the Astral Prism.
As for why Vilakis didn't kill Orpheus, it was because she needed him alive for his ability to block spiritual energy. This was key in resisting the revival of the Mind Flayer Empire, and also crucial to proving herself to the Githyanki, undoubtedly ensuring her rule over them.
