Prism Princess ~Futari no Himekishi to Kokan no Monshou~

In Prism Princess ~Two Princess Knights and the Mark of Exchange~ by Pajamas Soft, hikikomori Naoto's life turns upside down when a naked girl bursts into his room, strips off his pants, and proclaims, "Found you, son of the demon lord! Now die!" She swings a sword from thin air, only to be blocked by another nude girl who vows to protect him. Adding to the chaos, his childhood friend is an idol, and his little sister isn't just a chuunibyou but a secret powerful mage! What in the world is going on? Hau~ Omochikaeri!