魔王が元の世界に帰れないのは、俺の××が足りないせい？

The protagonist, a college student without a girlfriend, discovers a method to summon a demon during his boring spring break. To his surprise, a girl claiming to be a demon lord appears before him. She explains that she was summoned while escaping from a power struggle in the demon realm and asks for the protagonist's help to regain her powers and defeat her enemies. Reluctantly accepting her proposition, which is essentially a threat, the protagonist agrees to provide his semen as a source of power. However, both of them realize that they don't know the exact procedure. The protagonist offers to teach her despite his own internal confusion and raging sexual desire as a virgin.