The story is about Kei, a guy who accidentally hangs out at the lake where Mizuho appears when she gets out of her spaceship. But when he thinks of it as a dream, the next day at school the woman who takes over class is the same one as the one he saw at the lake!

Utterly confused, he still thinks it`s a dream, but when she moves in as his neighbour and he helps her out, things are really getting weird and they even are forced to marry because of it. But how do you marry an alien while nobody is supposed to know about the marriage - nor the fact that the woman is both an alien and your teacher?
Not even mentioning that the teacher/alien is a gorgeous woman ... and that some classmate already has her eye on Kei.