Tsuyokute New Saga

After the Demon King overruns the continent, swordsman Kyle leads a small party on a desperate mission to assassinate him. They succeed in ending the war, but Kyle is left standing among dead companions and a ruined world, wounded badly enough that victory offers him no future.

Inside the Demon King's castle, he discovers a magical relic that sends him years into the past, before the disaster began and before the people he lost were killed. Kyle now carries every memory of the war and a chance to prevent it instead of winning after everything is gone. Yet changing history requires more than knowing what once happened; every new choice creates events he has never seen, forcing him to grow stronger, gather allies, and hide the impossible knowledge guiding him.