This story is set after the contents of a Neutral ending, after Flowey is defeated. Frisk returns to the Underground for a visit.

This game's alternate universe is called UT!Soulscape, a world where the game mechanic of the battle box isn't limited to being a game mechanic. The box can be destroyed, of course, leading to Photoshop Flowey type battles.

In addition, monster souls can be attacked in similar fashions to human SOULs. The more Determination a monster/human has, the more saturated their SOUL. Sans and Flowey, of course, have the most. Each SOUL has a different color.

More lore coming soon!