Gedou Majutsushi no Hyouitan ~Saikyou Kenshi wo Nottottara, Jibun no Shintai wo Sagasu koto ni Natta~

Synopsis from ComicWalker.

Geol who've lived for long by changing bodies met with a dying swordsman. In exchange for taking the swordsman's body, Geol agreed to his request… As he meets a blind girl who treasures both Geol and Sigr, a new adventure begins–!!

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"It's about time I change bodies." A magician who lived for hundreds of years by taking the body of another was taking a stroll through the forest in search of a new vessel when he found a young boy who was on the verge of dying with a great number of slaughtered monsters before him. With the condition that the magician would protect Erena, the boy's companion, the boy let the magician take body. However, what the magician did not know was that the boy was the swordsman that had been expelled from the hero's party. [Source: MU]