Miku, Rin, and Len have been friends since childhood. And Rin and Len were twins. They had always been in the same schools and had never been separated from each other. So everyone would tell them they had such a good friendship

And by the time they were 16, they had to start a new school. And as usual, they would all go to the same school. So the evening before school, everyone was getting ready at their home