RS Keikaku: Rebirth Storage

Winner of smartphone novel company Every Star's MechaTsuku contest.

RS Project takes place in a parallel world that resembles modern Japan, but where alien lifeforms known as "Kikou" (Trick) fell from the sky ten years prior and started attacking humanity. The main characters are a pilot, Mizuru Mido, and her assistant, Fuu Sagami, who use a mecha made out of an enemy's remains. However, battle causes memory loss for the pilot, and they must unravel the mystery as to why.

(Source: Anime News Network)