Acero was born and raised in the kingdom of Atlas. For most of his life, he lived a quiet, albeit dull life. Ever since he was young, he would go to school, train, go home, rest, and repeat. His parents weren’t home very much due to them being on various archaeological trips, so the only people he could talk to were his older, very talkative sister, Talim, and their Faunus babysitter, Juno. Juno was a retired huntress that had come to know the Walkers by escorting them through various Grimm infested areas and ruins. She was a wolf Faunus that cared deeply for Faunus rights and was even a White Fang member when it first formed--she left when it started getting violent. Talim--who was 2 years older than Acero--talked about any topic she could think of whenever she could find an opportunity to, and Juno and Acero listened intently, but didn’t talk unless Talim stopped to catch her breath. Acero and Talim treated Juno with great respect and grew up with hatred for those who take advantage of Faunus, even starting fights because of it. This behavior carried on until they got severely punished by their parents and teachers. Acero had never done anything notable in his life--except beating up Faunus haters--until he got to Atlas Academy. He spent three years there, being trained and taught by both his professors and Juno. Acero found his weapon, Solar Centurion, his second year and started to unlock his semblance at the same time. Acero worked for a postal service when he wasn’t in school and started to save up money when he could, as he wanted to move to Beacon to avoid going into the military. Talim didn’t like his decision, but respected it, as she knew that the military wasn’t for everyone.
One day during his third year, Acero’s parents never came home weeks after their supposed arrival date. They were later found buried in the snow, 10 miles away from their dig site, along with the hunter that was protecting them. Their bodies had been torn apart by the Grimm, with the only discernible features being their clothing and their faces. Acero and Talim mourned the deaths of their parents. Juno also mourned their deaths, and helped the two siblings bury their parents. The three found the dead couple’s will and inheritance letter hidden in the house. The letter stated that Acero and Talim would split their fortune, and Juno would keep their house and its belongings, along with any artifacts that the Walkers found and kept on their journies. These included various weapons, armors, and valuable trinkets. Juno sold most of it to a museum, which allowed her to live the rest of her life in peace. Talim took two unique talwar swords with her as she left for the military. Acero went back to school pretty depressed, and anything his former team did to cheer him up failed.
Before he left for Vale, Acero asked his team if they could hunt the Grimm that killed his parents. They agreed and made a 2 day journey to the dig site. The Grimm ended up overwhelming the 3rd years and they were all badly injured, Acero being in the worst condition due to fending off a horde of Grimm to save his friends. Acero woke up a week later and was in a hospital. He couldn’t feel his left arm or see out of his left eye, but there was a feeling of cold metal touching his neck and upper jaw. His lower jaw, left eye and arm couldn't have been saved and were amputated as a result. Talim and Juno were crying as he looked at his new appearance, but Acero said nothing and looked at his remaining arm with a sense of determination. He looked at his caretakers and yelled at them to shut up and stop crying. This made the crying worse and he sighed deeply. The doctor came in and asked Acero if he would interested in prosthetic replacement parts. Acero nodded and signed off on the paperwork. Juno would would pay for these new limbs and the surgery about a month later. After about 2 weeks of recovery, Acero came back and finished his third year at Atlas. A week after school ended, Acero said goodbye to his friends and family as he left for Beacon Academy.
Recently, Acero was almost killed during a sparring match, due to a stray bullet hitting a bag of explosives that he was holding. He was rushed to the hospital and stabilized, staying unconscious for a few days as they treated the burn marks. When he awoke, Acero found himself in a similar, yet worse situation than before, parts of himself missing, scars all over his body. His sister and godmother came to visit him at Beacon hospital for a few days, crying over his newly disfigured state. After they left, Acero was visited by an official from Atlas. The official offered Acero new limbs and equipment, with a few strings attached of course. An easy option that the official gave was to sell out the schools plans for the Vytal Festival. The harder option was to do some paid, unaffiliated work for Atlas when he graduated, at least until the prosthetic's and new gear were paid off. Not wanting to sell out his new school and friends, Acero decided to take the harder option, and come work for Atlas when he graduated.