Merc Firewater was born Human parents in a modest fishing village on the outskirts of Cliffsunder. A deep blue Devilborn child whose appearance unsettled the household from the start, his childhood was marked by suspicion and cruelty. He was bullied by both the children and adults from his village, as well as his own sister Camas Firewater; but as he grew older, Merc began to explore the strange gifts of his devil blood. He discovered an inherent ability to create magic, using minor Spellcraft to prank Camas and the other children, though made sure his parents were not aware of his magical talents.

In time, he realized that while his magic came easily, control did not. During a period when Camas had fallen horribly ill, Merc decided to use his gift to conjure an illusion of a giant camas flower, his sister's name-sake. When he conjured this giant purple flower, it exploded filling the room in brilliant purple light, and somehow the stunning display instantly healed Camas. Stunned at Merc's power, the Firewater kids ran out of the house and played all day in the fields of camas together until their parents came home that evening. His parents thought her healing was a miracle sent by the divine, but the children knew that the devilborn was behind it. 

As a teenager, Merc helped his father on his fishing boat and brought the village's fish to the Grandport and up to the Middlecliff Market. He used illusions and cantrips to draw customers, disguise flaws in the day’s catch, and magically persuade competition to offload inferior fish; though his father did not like Merc's use of magic, he was willing to turn a blind eye if he did not cause an problems. Back in his village, however, the devilborn had few friends outside Camas and a few other misfits, who would sneak around and cause chaos.

Late one evening, seventeen-year-old Merc and his friends came up with an idea for a heist. Old Man Breagurd kept a strange little fish mounted in his dining room, said to bring him luck, and they meant to take it. After their parents were asleep, Merc and Camas slipped out, met the others, and crept aboard his ship. They found the fish above the table, small and brightly colored, and pulled it free. On their way out, a door slammed open and the group scattered, leaving Merc and Camas behind. With Breagurd rushing toward them, the devilborn panicked and reached for magic he had never used before.

He meant only to put the old man to sleep, but a sudden Wild Magic surge followed and seven bolts of force shot from Merc’s hand, killing him. While their friends had already began rowing away, Camas had seen everything, and ran from her brother. Their parents knew enough of his magic to understand what had happened, but could not excuse it. If the truth came out, the village would demand answers, and Merc would not be shown mercy; they decided he had to leave that night. Merc and his father packed a cart and set out for the city in the dark. Before he left, Merc tried to speak to Camas, but she would not look at him and told him to go to the Nine Hells where he belonged.

Money was tight in the family, but Merc's parents gathered their savings and sent him to the Whiteharbour Academy on his twentieth birthday. However, at the academy, the sorcerer found himself out of place. The structured, intellectual approach to magic clashed with how his wild magic manifested naturally. The harder he tried to impose discipline, the more volatile his magic became. One storm-lashed night, the devilborn received a later from his parents; Camas' illness had come back swiftly, and she had passed away days earlier.

His parents begged forgiveness, not wanting to risk Merc coming back to their village. Burdened by guilt and frustration, the devilborn climbed to the academy roof and abandoned formal spellwork entirely. Choosing to surrender to the chaos rather than resist it, he unleashed a devastating thunderous blast that destroyed his Spellbook and confirmed what he already suspected. The academy could teach him nothing. Acknowledging both his capacity for harm and his deliberate restraint, he adopted the virtue name "Mercy", a quiet assertion of who he chose to be that also played to his given name. 

Mercy left the school soon after, unable to return home, but by chance met Nessa Nina Quickpick Rumbauld Pennyluck, a former master Rogue. She convinced the budding Sorcerer to join the Whistledrop Crew, where he learned to help fence goods for them with his merchant skills; in this period, he found himself given a Cloak of Billowing. However, his lack of control over Wild Magic did mean he was not always chosen for more precise missions. Nonetheless, Mercy made friends with the various and diverse Crew members, and saw a future with them for a time. However, he was not present for the Ambush At The Whistledrop Hideout, and after the attack, Nessa Nina decided to disband the Crew, leaving Mercy in limbo.

 In the year after the ambush, the devilborn reopened a stand at the Middlecliff Market, and chanced upon a man who could help him control over his abilities. Stratus, a Windborn sorcerer, was himself an experienced user of wild magic, and took on the devilborn as a student. As they progressed through various training, he gifted Merc a Wind Fan, and the two bonded. Though his own wild magic manifested differently, Stratus helped Mercy learn to at least shape his own magic into more-desired outcomes, even if he could not attain full control himself.