Waku Waku☆Wakusei Princess

Hero was driving a car in the mountains. The car wrecked and he was self-pleasing while looking at the starts - one star rushed to the ground. When hero arrived to the crash site, the star turned out to be a spaceship. An alien girl princess Pam showed up from it saying that it was the energy generated by masturbation that had caused the ship to crash and that the hero was responsible for it and thus needed to help collect the energy.

The energy can only be generating by having sex with girls, so it needs to be repeated multiple times to collect enough amount.

[From vndbreview]