Sen’otome-tachi to Kizuku Moto-Teihen Murabito no Saikyō Hāremu: Sūmannin no Onna ni Taishi, Otoko wa Ore Hitori

The only ones left alive are us, the Valkyries. Oswald, a boy who had been scorned for his unusual magical power, awakens to find himself in a world several centuries after it was nearly destroyed by an evil god. It turns out that the sexual arousal triggered by Oswalds magic is the key to empowering the Valkyries. In other words it becomes a great power capable of saving the world!!