I Left My Magic Behind in Another World. A Terrible New Game for Little Sister Who Was Once a Genius Mage.

Synopsis

Mikan, a young girl transported to a world of swords and magic, grows up to become a great mage who saves that world from crisis—only to be sent back to her hometown, Niigata. Having lost her magic and companions from the other world, Mikan becomes a shut-in. Her older brother Itsuki, who has waited ten long years for her return, does everything he can to show her the joys of this world and gently coax her outside—but will he succeed…?! (Source: Comic Gardo, Translated)