Sinned heroes will save this world.. .A Dark Fantasy to be adapted to Anime.

Being sentenced to Heroship was the most severe punishment one could be given.
Heroes would be sent to the frontline of a never-ending battle against the demon lords.
Not even death could relieve them on their duty.
There was no end to prison sentence. Even if they fought for a hundred years, they would still not be released.
Only by killing every last demon lord would they be pardoned for their crimes.
And...that was no more than a pipe dream.
However, things might be different for XYRO, Penal Hero Unit 9004. He accidentally meets a goddess...and she asks him to be her knight!