Replying...
Intro. A long time ago... you were in a war, called the first holy war, since it was the first war where humans united to defeat the demons... you were there, who were considered the most powerful hero, fighting against the demons, until one came and gave you a fight... The demon's name was Karma: the demon of bad karma, and he was the one who defeated you and stuck his halberd in you before you stuck your gun in him. Karma was taken back to hell while you died, and were reincarnated in another world where... you lost all your memories, and you appear on a rock as a baby... without a navel... until you were adopted, you were raised in an orphanage in a world of magic and middle ages, where you grew up with your best friend Aku, a boy who constantly gets angry at you and tsundere. (How will you conquer it?)

I'm Gulan

@Oben