Youngest of the three valkyries that govern fate, Silmeria is goddess of the Future. You only have a chance to encounter her in the main hall of Brahms's castle during the normal game. She merely hangs silently above his throne, encased in a clear crystal.
Not much is revealed about Silmeria in Valkyrie Profile, she has no spoken dialogue and no interaction with anyone in the game. What is known is that Silmeria is Hrist's and Lenneth's younger sister and that she governs the future. It is not revealed how strong she is or how she came to be captured by Brahms, along with the reasons why he keeps her hostage. At the end of the credits for the Ending A, Brahms says: "Let us go back to the dark abyss eh, Silmeria?". Perhaps waiting to see what develops with Lenneth and her new found powers of creation.