Kei Kusanagi is living the life of a fifteen-year-old boy. He has a unique disease which causes his body to shutdown into a death-like state whenever he becomes too stressed or depressed. He calls this a "standstill". The amount of time he remains in a standstill is random, usually lasting a few minutes to a few hours. However, one time, he went into a standstill and didn't come out for three years. So although everyone thinks he's 15, he is really 18.
In the anime, Kei discovers that his new teacher, Kazami Mizuho, is actually an alien whose mission is to observe Earth. Due to a big misunderstanding, Kei has to choose between letting her secret out or getting married to her (he chooses to marry her). At first, he is hesitant about the whole ordeal, but eventually he falls in love and what ensues are comedic and dramatic situations which he must overcome in order to live a happy life with his new wife.
