Choukou Tenshi Escalayer

One day, a girl transferred into Kyouhei Yanase's class: his childhood friend who moved away when they were young, Sayuka Kouenji. While Kyouhei was happy to see her again, Sayuka seemingly pretended that he didn't exist.
Just then, out of nowhere, the evil intergalactic empire Dai-Lust began their invasion of Earth!

Upon seeing their advance forces, Sayuka rushed into a nearby back alley, where Kyouhei, having chased after her, found her absorbed in masturbation. He was so taken aback by this that he yelled in surprise, and Sayuka, having noticed his presence, immediately screamed in orgasm before being enveloped by a dazzling light that transformed her into Earth's mightiest warrior: the angelic Escalayer!

With her transformation complete, Sayuka soon drove away the army of Dai-Lust.

Having returned home, baffled by what he had seen, Kyouhei found himself being greeted by a girl named Madoka, who claimed to be a robot living with Sayuka. Madoka went on to explain that Sayuka acquired the necessary energy to transform into Escalayer and drive away Dai-Lust only by experiencing sexual arousal.

"I'm begging you, please make my heart beat fast!" said Sayuka to Kyouhei… and so their days of sex and war began. Their goal? The total defeat of Dai-Lust!