A synopsis about the game taken from Just Moe blog:
The story takes place on the continent which is divided into seven countries. Leo was born and grown up in a small village in the Reysol Kingdom. He, who is involved in a battle of Gods, leads his beloved people as a substitute soldier for Goddess that he believes in and keeps on winning battles against other substitute soldiers. From the earth to the celestial world where Gods live…. Leo and his company also visit the underground world where giants, who plan to destroy the earth, live. What they see at last is….
A manga adaptation of the game that's titled "Valkyrie Complex ZERO" started serialization in the male oriented bishoujo manga magazine CompAce on May 26th, 2009. The manga is drawn by Touge Hiro.