First and last lover

One day, an ordinary young man, Ichinose, is attacked by a beautiful woman named Moriya, who claims to be protecting the Earth from invaders from another world. Moriya tells Ichinose that the invaders are coming to Earth and tries to kill him, but Ichinose himself falls in love with Moriya's beauty at first sight!? Furthermore, when Ichinose expresses his gratitude to Moriya for protecting the Earth, Moriya suddenly begins crying... An ultra-fast love story that begins with the destruction of the Earth!