Chapter Text
Similar to classic Undertale, there was an infamous war that broke out between humans and monsters, that led to the humans victory. Upon their victory, the humans forced their enemies underground and sealed them under with a spell. Asgore, the king of monsters began advising them to build, create sanctuary in this prison they were put in, let is become more of a home and less of a prison. The monsters still devastated by their defeat and large loss in population due to the war, were hesitant to listen to their king. They sat around for days, picking at the underground walls and grieving before finally giving in and beginning to turn their miserable homes into a livable environment.
The monsters have been underground for generations, the Dreemurs being the oldest monsters among them all at about 167 years old, human years that is. Doctor Gaster is the second oldest, his title as the royal scientist giving him just as high of a status as the royal family. Gaster is about 154 years old. The royal children are both 14 years old, in human years. The monsters began measuring their years similarly to humans before being sealed underground, and it has stuck. Sans is the same age as the royal children, having been "birthed" a few months after the prince's birth. The fallen human, named Chara, fell down into the underground and was adopted by the royal family at the age of 11.
Papyrus, Sans' younger brother is 4 years old. In their home, Gaster has another skeleton monster, who remains nameless, take care of his children while he is at his lab across the city.
One day, before Chara fell, Alphys the assistant scientist had been rummaging around in the Waterfall trash dump, a place known for the amount of human garbage that filled it. Well, the scientist found books and vhs tapes titled with words like "The Stars", or "Space facts!". Not understanding anything in the media she found, she brought it to Gaster's attention, mentioning it in a passing conversation. But, Dr.Gaster took immediately interest and demanded to be given the books and tapes. He stayed in his lab for weeks reading and dissecting each second and word of the media. Eventually, about 4 weeks later, after a lot of untaken showers and uneaten food, he stepped out of his lab and walked home, stopping by the library on his way and handing them the books.
The popularity of the books sky rocketed almost instantly when word got out it was the royal scientist who had given them to the public. Monsters called him generous and admirable, when he had only given up the books because he simply had no use for them anymore and he preferred they not take up space in his lab. But, he took the compliments anyway, who wouldn't want free praise?
Over the next 5 months the underground exploded in spacey themed decor. Clothing being worn by every monster had some reference to a star or planet on it. Homes had banners hanging on the inside and outside, banners painted to look like the galaxies they had seen in the books. The crystals on the ceilings of Waterfall and Hotland began being harvested and used for decorative purposes. The gems were given the name "our stars" or "new stars", both terms coined by the monsters in reference to the crystals being the only stars they could see, sure they were artificial and not even real stars, but nothing could stop them from seeing these rocks as miracles. The entire underground saw the new stars as the universe blessing them after their misfortune of getting shoved and sealed underneath the surface. It became their culture. Wear the crystals, decorate with them, sculpt them, eat them. They were the very thing that gave the monsters a sense of purpose, it wasn't a strong one nor could any of them put it into actual words, but fuck it, they all felt it anyways.
Even the king and queen grew into the culture, collecting their own stones from outside their castle and commissioning rings made with the crystals. Once touched, the crystal then binds to that monster's soul, so each monster essentially gets one crystal, that's it, it will not re-bind to another soul. When making jewelry out of the stones, if traded, say the king wore a ring with the queen's crystal on it, that would permanently bind their souls for eternity, and of course the queen would have to wear the king's crystal for the bind to be completely permanent. When binding with crystals it's important to keep in mind that the bond will not happen if the souls being bonded refuse to bind. There is a level of consent required in a true bond, and once given there is no regretting or turning back because you're souls will now forever be tied to each other. Once bonded, the pair begin to feel the other's soul vibrations much more clearly, making them able to speak almost telepathically, just without words. The vibrations from soul to soul let one partner know how their other half is feeling immediately. Any pain one feels is felt by the other, similar to a voodoo doll. If one soul shatters while being bonded then the partnered soul with begin to wither, leaving the monster fainting into a fallen down state until their soul finally shatters. Each crystal has it's own color after being assigned to a soul, and that color dictates a main soul trait. Similar to human souls with the coloring signifying a specific trait. Most monsters with the same colored crystals tend to partner up and bond together, but partnering outside of your crystal color is perfectly normal as well.
Human souls are already colored when reaching adulthood, but not when they are born. When a human is born their soul is white, similar to a monster soul. As the human ages their soul slowly begins to color overtime, usually becoming vibrant around the ages of 16-18, but sometimes the vibrancy can come early.