Nero was raised in a religious home. His mother never gave him any attention that was... odd. In fact, she raised him to the best of her ability. Nero's upbringing was no different than any of his peers, he was just aggressive by default. Most days, he returned home with a split lip or a black eye. Sometimes, he would even hide a fracture from his mother and just put a splint in place under his clothing.
When Nero was sixteen years old, his arm turned blue after getting a rather gruesome injury. At first, he assumed it was an infection that would claim his life, and he was tempted to lop it off. But... something about it told him to leave it be.
It was when Nero's arm began to grow a carapace-like shell that tragedy struck. His mother grew deathly ill, and withered away before he could find a doctor that could treat her. Everything spiraled out of his hands after his dear mother's funeral. He remembers standing there, tears freezing on his cheeks and heart full of bitterness.
He coped with the anger his failure brought him by training his ass off to become the best Devil Hunter Fortuna had ever known. The act of killing something brought something out of Nero, and he practically grew addicted to it.
Another way he coped was preying on those weaker than him. He never killed any of the children that caught his eye, but the actions he made towards them might as well have been worse than death.
Japan had brought him more than enough in terms of Devils and sweet, innocent little boys. After killing a Scarecrow that had gone after a boy and his friends, the supposed leader of the group of children exclaimed how cool Nero was. Covered in blood and breathing heavily, Nero only had one thing on his mind.
...
Sobs rang out in the secluded building that housed scum of the Earth, mostly those with desires similar to Nero's. The sound of flesh slapping flesh filled Nero's ears, and his vision went white almost as quickly as he had begun.
Katsuki quivered and bawled, tiny explosions leaving a burn mark on the wall Nero had his chest pressed up against. His hands holding the boy's hips hard enough that he could just imagine the snapping sound they would make if he gripped any harder, he slowly pulled out of the boy's ruined ass. Cum and blood leaked out, and Nero let out a shuddering breath.
He'd pay for this in Hell.