Suterareta Tensei Kenja: Mamono no Mori de Saikyou no Daima Teikoku o Tsukuriageru

At his death, the great sage used the new magic he developed to reincarnate into the future. However, he was deemed to be talentless and abandoned in the forest of monsters where he was picked up and raised by goblins. To repay them, he helped them evolve and taught them magic. The story of the abandoned child who will build what would be known as the great empire of monsters.