I Was Exiled from the Heroes' Party So I Tried Raising the Demon Lord to Be Unbelievably Strong

Reisel is summoned to another world as a hero to fight the demon tribe, but he ends up being rejected and banished because his combat power is measured to be nil. However, this was actually a misjudgment by the measurement device, because he is so overwhelmingly strong that no one in this world can match him. After his exile, Reisel travels around the world, learning that the demons are not so bad and decides to join them instead. The world situation gradually reverses, as the demon tribe that took Reisel in as a friend prospers, while the kingdom that banished him falls into ruin. (Source: Futabasha, translated)