終活勇者, End-of-life hero, The End of Life Hero

Several decades have passed since the hero defeated the demon lord and peace came to the world, and the hero has grown old enough to only vaguely remember magic spells. When the remnants of the Demon King's army attack the hero, he decides to set out on a journey again. This time, it's not a journey to save the world, but a "departure journey" to look back on his life.