On the ending screen, do not press any buttons for 30 minutes. After 30 minutes, press a button and "PRESENT FOR YOU" will appear on the screen. You will then go to a bonus map.
At the game save screen, select the fourth slot, then enter Ootani Tomoko as your name (in Japanese, of course) or Abe Hiromi then before entering confirmation option, hold A or B or both on the second controller.