Seiken ga Saikyou no Sekai de, Shounen wa Yumi ni Aisareru: Fuuin Sareta Maou ga Kureta Chikara de Seikenshitachi wo Engo Shimasu

Long ago, humanity was defeated in a war against demons led by four demon kings, and only managed to survive on what little land remained under the protection of seven holy swords. Humanity continues to fight against demons that attack them, wielding many "imitation holy swords" made in imitation of the seven sacred swords left behind by the goddess. This is the story of Roy, a boy who is branded a "dropout" in a world where holy swords are supreme, and the strongest and worst demon king sealed away by the four demon kings; together, they will save the world. (Source: Kadokawa, translated)