The Side Story, so far, covers what happens in between the Main Story chapters. Players can buy it in the Shop just like the full game/any other extra song pack, but these chapters don't count as part of the main game and must be bought separately. Songs in the Side Story chapters also have to be played in chronological order - just like in the Main Story - and they come with cutscenes and narration.

Currently, the Side Story is made of these two chapters: