Mushoku no Tensei - Eris Gaiden

Eris Boreas Greyrat sets out on her own after realizing she needs to become strong enough to support Rudeus, her cousin and traveling companion. Once an honorable young lady, she has grown into a swordswoman since the two were transported to the opposite side of the world. When Rudeus comes close to being killed, Eris cannot save him. Determined to become someone who can protect him rather than rely on him, she leaves and begins her own journey. This side story branches off from the main Mushoku Tensei manga around chapter 51, corresponding to volume 6 of the light novel and the first season of the anime.