The second in the Light RT subtype of Reyvateil enemies, these foes are much stronger than their predecessors, the Light RT As, although since they are only featured in two of the boss battles against Mute, you won' have much of a chance to see them in action, and most likely will be outclassed by the normal encounters you will have at these points in the game. Therefore, just get rid of them so you can concentrate better in the boss.