Note: This was written before the other chapters of Deltarune released and has been altered from the cannon to fit this AU ( IE: The Dark World is a part of Ultra Space in this AU, The Prophecy is different from the cannon, and the fountains are linked to Necromza).

When Necromza lost it's light, pieces of it were scattered all over both the Lightner World and the Dark World. The fragments in the Lightner world become Z-crystals while the fragments in the Darkner world would form Fountains.

These fragments still housed light, laying dormant unless disrupted by a magical source. Causing them to expel said light into a concentrated beam, forming a Fountain.

Fountains didn't just spring up everywhere once these fragments landed. Only one did naturally form and that what the Dark Fountain in Castle Town, which would go on to provide a source of light and energy to the whole kingdom for centuries.

When Necromza escaped it's containment. It traveled to the Dark World in search for light, coming across the Fountain. The Blinding One attacked, draining the Fountain of it's light, leaving the castle and capital in ruins.

For a while, the Dark World was thrown into hysteria. Corrupt individuals saw this as an opportunity to take power. One in particular, known as the Knight managed to do so. By uncovering other fragments to create artificial fountains and allowing those who pledged allegiance to them to control said fountains.

Eventually the Knight was defeated, the fountains sealed, and order was brought back to the Dark World. A small town was built on the outskirts of where the old castle stood, named Castle Town. The Necromza Fragment that powered the Dark Fountain would be made into a statue in memoriam to the royal family and their lost son, Ralsei, whom ended up in the Lightner world as a result of the incident.

The castle ruins would later become a thriving home to Pokémon and Ultra Beasts. Being barred off from the public.

By the time Selene crash-landed in the Dark World, a new Dark Fountain had already been created from an uncovered Fragment.