Sundome!! Milky Way manga volume 2 features story and art by Kazuki Funatsu.

The beautiful alien Lune has come to Earth in order to be inseminated by Yoshitake, the world’s horniest man, and thus save her species. But whenever Lune grows aroused and embarrassed, she transforms into an inhuman monster. Her sister arrives on Earth with worse news: if Yoshitake loses his virginity to anyone else, Lune will be dragged home and face the ultimate punishment! Meanwhile, Yoshitake plans to use a company trip to an exotic resort to put the moves on his naïve colleague, Yuizono!