The Save Everyone Route is only possible to start after completing the True Pacifist Route, after which you will obtain an Aries Card, the key to starting the route. At the name entry screen, you must enter "Chara", and the display will ask you whether you want to begin the 'secret ending'. Instead of spawning at the starting area, you will appear directly outside the Throne Room in New Home. You will meet Chara in the Throne Room, who will battle with you, but after sparing them repeatedly, they will warp you to the end of a True Pacifist file at the starting area. In the midst of the warp, you will be forced to battle with W. D. Gaster, but after successfully sparing all of his various attacks through time, you are presented with the opportunity to sacrifice your soul to Asriel, and therefore, save everyone. If you do not have all of the Constellation Cards, the second part of the Bedtime Story (only accessible after a Save Everyone Route is completed) will not play.
Attempting to reset a save file after completing a Save Everyone Route will play the song "Arial (Checkerboard Memories Arrangement)" and display "* ..." instead of "A name has already been chosen.". Selecting Yes will perform the reset, but crash Outertale.