The Hero Is Overpowered But Overly Cautious, Vol. 6 (manga)

It's time for the final battle against the Demon Lord! ...Or at least, it's supposed to be, but Seiya suddenly goes missing while the rest of the party is taking a short breather in the imperial capital before the moment of truth?!?! They'll have to track him down-and when Ishtar reveals the secret of Seiya's past, his uncharacteristic rashness starts to make a lot more sense...