Shiryoujutsushi Weltz no Heiwa-ron

In their quest to achieve world peace, the Hero's Party has succeeded in defeating the Demon Lord at the journey's end. But victory came at a heavy cost - the Hero, the Saint and the mighty Warrior all perished, with only the Sage, Weltz, as a sole survivor of a hard-fought battle. Thanks to their sacrifice the world peace has been achieved... or so it should have. Two years later, the world has never been in a worse state. Conflicts between human kingdoms have erupted, and the Demon Lord's army remnants became more relentless than ever. As the last surviving member of the Hero's Party, Weltz is forced to bear the weight of the world’s problems alone. And so, in a desperate bid, he chooses the one path that should never be taken—!!