Shinobi Grim Dawn

A world that survived the Apocalypse. A world invaded by hordes of demons from other dimensions. They invaded and were repulsed.
Two men who with their deadly art paved the way for humanity to win. Two people who were no longer needed after the victory.
Fate gave them a second chance in another world. A world where people like them are respectfully called S-rank. How will the history of this world change if the place of those who were to define it is taken by a sword master and a necromancer?