Plenu Ryunu is an ARM owned by Lilis. It has a non-specified type and is very unique and powerful. It can fire some defensive blue energy beams, but it's main power is the ability to manifest people's imagination as real things.
This was used to create a phantom army that could hold off the combined power of Alviss, Jack and Nanashi, as well as creating an entire replica of Tokyo including believable imitations of Koyuki, Kotomi, a replacement older sister for Dorothy and a white-hatted damsel for Alan.
Babbo and Alan both believe that Plenu Ryunu eventually gained a will of its own, much as Babbo did, but in a different way.