The world has been saved, but I picked up a girl with amnesia

"Show me the world!" A hero, burnt out after defeating the Demon Lord, falls in love at first sight with a red-haired girl who is being chased by a mysterious enemy. He tries to help her, but the purpose of her pursuers is unknown, and she has amnesia! What in the world is going on with this innocent-looking girl? To find out the girl's secret, the hero sets off on a journey to visit his friends: a black-hearted sage, a brainy knight-princess, a 1,000 year old little girl, and a filthy-rich necromancer. His infatuation intrigues his former party comrades. "Who is that woman?" they keep asking him, even as they reunite to defeat incoming assassins one after another with their unique skills! But just as they finally track down the mastermind, they are told, in a very threatening message, "If you fall in love with the red-haired girl, the world will fall." Whoever you are, I will save you. A retired hero traces the past of a mysterious girl with the strongest party. A re-life fantasy begins! (Source: TO Books, translated)