Forbidden Love ( Imouto de Ikou ) Episode 1 - Forbidden Love

When her family is overthrown in a coup d'état, Princess Mayuka is sent to Earth to recharge the Ultimate Weapon. After studying the mating behaviors of Earthlings, she decides to enlist the help of one of her research subjects, college student Yoshizumi, but crash-lands on his roof. Taken hostage and shot with her own gun by Yoshizumi, she is brainwashed into thinking she is his younger sister. Fortunately, Yoshizumi grows fond of Mayuka and decides to help her with her mission: to awaken the powers of Akiho--the red-haired, green-eyed, appetite-driven Ultimate Weapon--using "primitive stimulation"

My name is Mayuka and, although I look like any college schoolgirl, I'm really a princess from another planet! With the help of my dear Yoshizumi, we are on a quest to restore earth's most powerful weapon to help save our mother. Unfortunately my weapons were taken away and I'm left helpless and defenceless! What will happen to me? Watch and find out how I use my own resources to save the day!

A fleeing alien princess arrives on Earth to revive the ultimate weapon, a weapon that needs sex.

Forbidden Love ( Imouto de Ikou ) Episode 1 - Forbidden Love