Innocence Dies Young
She was even four when she learned how to use a gun.
The first time she shot it the recoil caused her to hit herself in the head with the gun, leaving a small cut just at the start of her hairline. Her trainers didn't even let her cut get cleaned before they made do it again. And again and again and again, until she got ten bull's-eyes in a row.
They said that she was an Asopportare and could handle it. She didn't feel like she could.
The next day they had her do the same thing but this time she had to get twenty bull's-eyes in a row. It took her a week of eating nothing but bread and water until she could shoot twenty bull's-eyes in a row.
This continued on for weeks until she could hit moving targets, shoot while under fire, and still hit bull's-eyes every single time.
Then they moved on to different types of guns, hand-to-hand combat, sword fighting, explosive making, espionage, and finally using her flame.
During her fifth birthday party, an enemy snuck into the house and tried to kill her. On autopilot she reached for the gun lying under her pillow and shot him in the head. Her first kill and it happened on her birthday.
She cried for days and refused to come out of her bedroom, but they finally got in and dragged her out to the gym to resume her training with a higher intensity level.
All this continued on without pause, even when she found her father's dead corpse out by the front gate of her house. She didn't cry then for she knew it would only make everything worse.
Her father's death caused the family to become more paranoid then ever that everyone was out to kill the Asopportare heir, Chiara. So after her father's funeral she was moved to Namimori with her first Guardian and the training continued, but this time she had something to look forward to. Or rather someone who could brighten up the bleak existence that was now her life.
His name was Tsuna-kun and he was excited to see his friend again.