Choi Kuzu Shachiku no Isekai Harem Kenkokuki

After working himself to death, Kou Asagiri wakes in another world. A goddess asks him to help save humanity, restores his youth, and gives him a fresh start. While learning magic and surviving in the wilderness, he begins building a place of his own—until an encounter with the elf Luna sets his new life on a very different course.

(Source: CLLENN, translated)