ZeRoN's Grate ~ The Story of an Innocent Demon God

Is the boy an angel or a devil?
In order to find the one and only heart, the four hearts now set out...
A world where the scars of the great war remain. Akari and Kenta are forced to work in the black market, but are caught up in an attack by a runaway robot. The one who saved it was a boy named Zeron. He is looking for the strongest robot soldier, Zeron-type Heart, who disappeared during the last war. The journey to find the legacy of hearts sleeping in the world begins now...