The unforgettable car accident happened when they're still little. They are touring for their field trip to have fun but on their way, a big truck was accidentally bumped onto their car...The six boys (Youngmin, Kwangmin, Minwoo, Jeongmin, Hyunseong, Donghyun) survived but the parents of the twins died on that tragedy...One them lost his memory, Youngmin and all of them the memory of that accident still remains in their life and the only one wh