Blue Drop - Tenshi no Bokura

The Arume, a dominating alien race of female humanoids (alien lesbians) has conquered Earth. With total control over the world they have begun live experiments on humans.

One day, out of the blue, a girl that Shouta Yanami has never seen before in his life arrived at his house asking to have sex with him. It turns out that his best friend Kenzou Sugiyama was turned into a girl in an experiment to create a child between a man and a man who turned into a woman (transexual) and a straight male and now he has a week to have sex with him/her or he will be eliminated!