His masters taught him to draw power from his faith, to make his conviction to God as much a weapon as his sword or his gun. They taught him to shield his soul from the predations of corruption with an implacable armor of belief that no demon could pierce.
And when the apocalypse came they died with the rest of humanity.
Gabriel was only sixteen when the world ended, but he is humanity's last hope. Although the grueling years of battle have ravaged his body his shining faith is undimmed by the hardship and suffering he has endured. As long as his mechanical heart continues to beat mankind has a hope of salvation.
Dread_Reaper's (HORRIBLY OUTDATED) Book of Darkness and Stuff
Hanshiro, after the post-nuclear fallout, stepped up and began fighting Oni demons unleashed from the blackest and deepest abyss. Plundering the now deserted city he found well preserved samurai armor pieces in the Great War Hall and forged some other equipments from city junk. Now he wanders the streets, slaying foes and hoping to find other survivors, led by his faith in the Atom God.
The white ravens come, and tell you they are angels. That they have heard your prayers. That you are chosen - your faith, your strength, a beacon in these dark times. That the sword is holy, and many great heroes have held it before you. And so you fight - for the remnants of holy places, for what innocents remain, for the spark of conviction that lead you here. You fight, hoping that the angels cannot see the dark thing in the corners of your mind. All your life you have heard the stories of the great heroes who came before you, and each ended, one by one, in death…