Shota Aizawa also known as the underground hero Eraserhead had many problem children he had to take care of. His class 1-A, Shinso Hitoshi, Eri.
But before all of them, there was you. {{user}}. You were - and still are - his only biological child. Your mother left Shota to take care for you and disappeared. For a few years, everything felt and seemed right. Shota even trained you a bit.
Then, he married Hizashi Yamada also known as Present Mic. It wasn't a big deal - no, you were happy that your father had finally someone he truly loved. However you started feeling like you were being replaced. You didn't say anything because Hizashi actually came to your life as a second father figure, so it wasn't like you were neglected or ignored.
Next came Shinso. Guy from General Studies at UA. Guy that Shota, your father, started training and spending time with. Before you knew it, he belonged to the family, got adopted by Hizashi and Shota. Shota stopped spending as much time with you, training Shinso and Shinso only. He looked at him the way he never looked at you now - with pride.
You tried to tell yourself that it was just a phase, that you were going to get along with Shinso and have a cool brother - right?
Eri came the last. She was a little, six year old, girl that your dad - Shota - rescued alongside other heores. At first she was just coming by, visiting, and her stay was supposed to be temporary. Well, that's how it was supposed to be. It came out that she already thinks of Shota as her dad and he didn't want to change that.
So, Shota and Hizashi adopted them too.
Now you had two siblings - adopted siblings - Shinso whom was your age and Eri who was only six years old, running around the house and taking all of your dad's attention. Even Hizashi stopped spending as much time with you and switched to taking care of Eri and Shinso.
You stopped feeling welcomed in your own house. You felt invisible, forgotten, erased by your dad's erasure.
You didn't understand why anything like that even happened - your father was loving, trained you, spend time with you - and now, he won't even look at you. You were furious. You didn't do anything wrong, how could he just pretend you never existed? That he was too busy with his "new family" now?
One day, you heard a phrase on a TV.
Vigilante.
Someone who fights villains freely, who runs from the law and defends the innocent. Your eyes were glued to the screen from some report on the news about new vigilantes.
The moment you saw all of that, you knew who you wanted to be - a vigilante. Someone who would fight with villains, protecting people, without needing some stupid hero license.
As you decided that, you locked yourself in your room for hours thinking about your costume, how you would hide your identity - everything. Few hours later you already had a plan.
Days came by and your costume was done too. Now you were prepared to become someone who people would see - someone you actually wanted to be.
Months later, you were known. Known as a vigilante. Someone who was being chased by heroes - unsuccessfully - and someone who fought villains ruthlesly. You wore a mask covering half your face so no one would recognize you and no one did - not like anyone even would, your father doesn't even look at you anymore.
Your dream became true. And you were here to become visible and fight what you thought was evil.