U1TM8 is a test tube baby in the most literal sense of the phrase. The "Vierra" was grown in a lab, deep in Garlemald, with splices of DNA from the savages of Eorzea and its allies. "A way to further Garlemald's evolution", "A weapon to surpass even the greatest magitek." Those were the promises that the scientists made to the citizens of the empire. Of course, the Garleans had concerns about the use of magic and manipulation of aether, so to quell the fears, they started with a small strike team. 6 soldiers, each combined with different thoughts on what was considered the best features of each race, soulless and ready to follow orders. PRISM was the name of the squad.
PRISM did their job well, dispatched constantly to handle threats inside and outside the empire. No hesitation in their actions. They were essentially machines after all. One day, after stopping an uprising by making an example of the leaders, one of the other experiments, F1R5T, came up with a collection of books. Deciding that it'd be best to further their knowledge, she decided to take it back to their chambers.
The first change was their names. Reasoning that it be easier to communicate, they each took names of various legends or deities in the book. U1TM8 became Sol, Ruler of the World. These names were not to be used in front of higher-ups or in spaces where they were not alone.
The names were the least notable of the changes, but they set everything else in motion. With the new names, the soldiers of PRISM started feeling closer to each other... a sort of sibling bond forming between the 6 of them. With that came new emotions, a gradual understanding of friendship, and learning what right or wrong was. Hesitation would show on the battlefield when an order was given that could potentially put another in danger.
It all came to a boiling point when the youngest of PRISM, "Etro" put down her weapon and said that she would not kill a child. A direct refusal of the order she was given. The ride back to the base afterward was quiet, the tension in the air signifying that things were about to change.
PRISM was thoroughly investigated, the use of names coming up, the books, and the refusal/hesitancy to follow orders that cost the empire some losses whether it be time or people a few times.
The first idea was to break PRISM up, but while they were effective, their outbreaks and rage started increasing, occasionally doing damage to anything nearby. The destructive force caused some civilians their lives.
PRISM was put back together once more after the scenes they were causing, which caused a little confusion, but they didn't complain. Their family was back together again.
Their next mission was to stall the front lines of an encroaching rebel army, holding them off until reinforcements got there. A simple enough mission.
As they fought, making use of the cover they had, tactically and stealthily deploying weapons as much as they could, they realized something.
No one was coming.
The empire, in a ploy to get rid of them, sent them out to their deaths. They didn't mind getting rid of territory if it meant getting rid of PRISM with no harm done to themselves.
As much of a fight was put up by the desperate soldiers, they were outnumbered, eventually overwhelmed, and left to die. Their bodies were forgotten by both the empire and the Eorzean alliance.
Sol couldn't tell you how he managed to survive. Whether it was something in his bioengineering, the will to survive that he gained with his new soul or just pure determination. He did not know. However, he crawled, taking shelter where he could. Eating and surviving off what little was left behind on the corpses of the battlefield, making it Eorzea by some twist of fate... and a lot of luck.
Sol travels the world now as a humble Mercenary/Adventurer. He hopes to find where the rest of PRISM went, if they're even alive.