Hero Is Overpowered but Overly Cautious, Vol. 5 (light novel)

Beast Emperor Grandleon, Machine Emperor Oxerio, and Vengeful Empress
Celmonic have all been vanquished. Seiya and Rista venture to the sand territory
to face the last of the Demon Lord's forces, but are wholly unprepared for what
they find. They are greeted by an alternate Ixphoria where Seiya never lost to
the demon lord, and he and Tiana are living a happy life together; the future
that could have been...