Moritoki is a third year high school student attending to Hoshino Academy who's especially good at sports. Another peculiar thing about him, is that there are three female childhood friends of his attending the same school.

Back in the days when they were children he and his childhood friends exchanged a promise, which Moritoki actually forgot.

On the day of his eighteenth birthday, all three of his childhood friends wait for him in his home, wearing wedding dresses. Much to his astonishment, they remind him of the promise he made: "When I become an adult I will choose one of you to become my wife".

Because he forgot all about it, they postponed decision time by one month. What will Moritoki do? Who will he choose?