Saikyou no Kenjin, Henkyou no Mura Musume ni Umarekawaru.

The Legend of the Reincarnated Sword God: From Hero to Village Girl The continent was once ravaged by a war of invasion led by an evil empire. The man who ended the slaughter by slaying the Emperor was the legendary hero, Edgar Knightsword, known as the "Sword God." However, even the man called the world's strongest swordsman could not defeat old age. After entrusting everything to his disciples, his seventy-year life came to an end. But when he opened his eyes again, he found himself reborn as "Linne," a young girl living in a remote border village! Now, the new legend of Linne—the world's strongest swordsman turned little girl—begins! https://mechacomic.jp/books/198206