Kyuuseishu No Ikinokori summary:

In order to stop the invasion of the demons and seal the evil god which has been resurrected after a thousand years, Grey embarks on a journey together with his sister, Fiona, and his comrades. At the end of their journey, they were facing the evil god, and all of his comrades including his little sister were killed because of the evil god.Being the only survivor of the journey, Grey was hailed as a hero and was granted the throne as the emperor of the holy empire, gaining glory and authority. Unfortunately, Grey couldn’t recover from the grief of losing his one and only sister, and decided to use any means necessary to revive her. After countless attempts to try and revive his sister, Grey became hopeless, until he heard a mysterious voice saying,After making a deal with the mysterious voice,Grey found himself standing in his hometown that was supposed to be destroyed by the invasion of the demons…