Giniro no Olynsis (Light Novel)

is the light novel adaptation of the 2006 anime-original series of the same name. It is written by Hitomi Amamiya and Illustrated by Hisashi Hirai. It was released under the Dengeki Bunko Imprint in December 2006.

Synopsis
AD 3567. Mankind has lost its once great civilization, now living in the ruins of the aftermath. But even though their lives are threatened by Gardeners — mysterious unmanned mobile weapons (of different ranks) sent from the Moon — brave teenagers have to become Gardener hunters to earn their living. And although human civilization at large lies in ruins due to high-tech maintenance free technology, some parts of the remaining cities still work in limited ways, supporting the humans living there.

One fateful day Tokito Aizawa meets Tea, awakening a power older and beyond that of the Gardeners, and inadvertently opening up the door to a possibly much brighter future for the remainder of mankind...

(source: AniDB)