Born in the Drow society in the underdark Erza was thrust into danger since before his eyes even opened.
Being the heir to a noble family he already had enemies even before he was hardly minutes old.
He survived his first assassination attempt when the assassin was foiled in her attempt to poison him in his crib hours after he was born, this was the world he was thrust into.

Growing up was a struggle aside from the constant attempts on his life. Everyone criticized his mother for not having a girl and his mother seemed to despise him anyways, he was teased mercilessly among the other boys by the girls who lorded their superiority over them.
But under the tutorage of his father, his mothers spy master, and their battle mage he learned how to fight and use magic early on in order to fight off the girl led gangs that roved around tormenting others.
The boys around him always idolized and worshipped the girls, pinning for their affection and thus willing to do anything they commanded. This was totally natural in Drow society since they saw their fathers and male slaves do much the same.

When Erza turned the Drow equivalent of eighteen, he inadvertently made himself an outcast and thus a target for bullying and even outright assassination attempts by the other children. A girl saw him and his beauty caught her eye, so she wanted him to go with her somewhere they could be alone and he could pleasure her. She was beautiful herself and Erza was tempted, but he ultimately refused which earned him her hatred and thus the hatred of all who knew her.
This was a time in his life where he fought the hardest, fought for his life, fought for his honor and dignity.
Some of the other outcasts began to notice him and over time banded together to form their own gang where they could protect each other.

During this time Erza's younger sister was well on her way to inheriting the noble title, and Erza himself was looking at either servitude, assassination, assassination training, or military service. He chose the military and began a steep climb through the ranks, a climb that took years of blood sweat and hardship. But over time he gained good favor and support from his female superiors, using every recommendation and pulling every string he had access to, he eventually became commander over his own squadron. An army of Drow men and women loyal to him and willing to follow him to the death.

He built his own house and noble crest, separate from his mother who assumed he was dead by now.
And now he forms a strong arm of the Underdark military, wielding power and influence backed by his army.