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.

Abandoned by his mother and grown up in different orphanages, the only thing Kamishiro Maiku has left from his early childhood is a photograph showing the house he was living in and himself and a girl playing in a children's pool.

When Maiku recognizes that same house in a TV report about an UFO sighting, he decides to travel to that peaceful town, search for the his childhood memories and start living by himself, in that house he's so far only seen in the photograph.

One day, however, Miyafuji Miina and Onodera Karen burst into Maiku's life. Both have the same eye color then Maiku and each has a copy of the same photograph showing a boy and a girl playing together, and each of the two girls introduces herself as Maiku's twin sister...

Who's the twin? Who's the stranger? Look forward to a joyful and romantic drama about these three twins.