Don't hide from me ~ Izaya x reader

Teaser: Missing for three years?

At the age of 15, [Name] disappeared from the HQ. Everyone thought she died.

Dear diary,

Sorry I splattered blood all over you. Now your pages are all red and the foul stench! – Sorry.

I don't know why I'm bleeding. Or maybe I do...?

My heart is pounding loudly and I'm sweating like I took a shower. I'm holding a doll as I'm writing this and I've locked my dorm room door.

I can't let anyone else know of this. The thing is my mother wants me dead. She's after me. I once opened the dorm door late night a few days ago while everyone was asleep and you'll not believe what I saw. All the other doors were closed and at the end of the dark hallway were two pairs of eyes staring intensely at me. And I could hear this strange moaning noise and it is the same sound my mother makes when she is asleep. I don't know why she makes those noises but she says weird things like... "Kill him" and "An informant" and says my father's name... "Isaiah..." but that's not all... when I opened the door that day, she was spelling out another name "I-Z-A-Y-A."

Who is Izaya?

Someone is banging the door. I need to –

The rest of the diary entry had blood all over the rest of the page. That was the last diary entry from [Name]. Nobody knows what happened to [Name] after that, but demons in their dorms heard her screams across the hall that night in the HQ. They tried to open their doors, only to find it locked from the outside. The next morning, demons found deep trails of scratches on the hall floor, some theorizing that they were made by [Name] as she was dragged across the hall.

Everyone thought she died. But then, when all her demon friend graduated from the HQ, they were sent to Earth to continue on with the rest of their life.

They found [Name] living with her mother.

For three years, [Name] had been missing from the HQ and the headmistress had not done anything for it, but instead sent her to earth? Why? – That being said, did the headmistress send her to earth, or was she kidnapped (considering the nail scratches on the floor)?

But as mentioned before, the graduated demons forget about their times in the HQ, and so they forgot everything about [Name]'s disappearance and never questioned her.  

[Name] along with her demon friends all moved to Ikebukuro and opened a cake shop. The (currently unknown) headmistress sent Amaya Mori to work with them since she had no other way to earn money. Now two things happen when you turn 40 as a demon. First, you can be granted with magical powers if you've worked hard enough for the past years. However, if you haven't worked at all and have lived as a normal human being after graduation, you do not get granted any power at all with no weapons. Nobody knows if Amaya Mori has magic or not, since she never used them.

What exactly happened during [Name]'s past?