(A/N: This theory was based on FNwH's easter eggs and in my own thoughts on about the happenings in the past of the resto. Names mentioned here, aside from Herobrine and the Gang, excluding the manager, Randy, were the only real names in the game itself.

This story was also based on FNaF's lore, but wasn't related to ANY theories/stories of the latter.)

There was once this man who made a family-centered/entertainment restaurant in 1970, that is, Cake Family.

At first, he only had one animatronic, and that is, Zombrine.

(This would rather explain why in the Custom Night, Zombrine had blue eyes instead of white.)

This just attracted a very few people, and business was very bad for the management.

So they decided to make new animatronics, PigZombie and Chicken.

This would eventually invite people and the resto became famous.

In the 1980's, the owner eventually had a son named Herobrine.

Herobrine was a very talented child: he can sing, dance, and play the guitar and piano very well. Aside from these, he can make animatronics, program them, and was a very intelligent boy, always topping his classes. He was also a very hardworking, humble boy.

His father was indeed very happy, seeing his gifted son also serving on the resto, playing, singing, dancing, and making people happy, especially children.

He was happy, that he had a son like Herobrine. He was very proud of him. They all lived happily, until the year 1987....

It was Herobrine's father's birthday, and he decided to surprise his dearest Dad.

He made an animatronic that looked exactly like himself, but had blue eyes.

His father was very joyous, seeing his clever, 7-year-old son's wonderful creation.

They had a party afterwards.

Little did the people know that there was a lurking killer nearby, along with his own son.

Herobrine was alone. Completely alone, with his toolbox on his hands. He was walking innocently by the West Hall, when, all of the sudden, a man and a boy pounced on him.

They both dragged the helpless boy to the Supply Closet, and to the Back Stage.

There, Herobrine was mercilessly killed.

His father totally didn't know, until he noticed that his dearest son was missing.

He roamed all around the place, with his employees, to find for his son.

On the moment they opened the Back Stage, the father screamed in horror and grief at what he saw:

His son, stuffed inside the animatronic that he,himself, created, blood flowing out from the joints.

Herobrine was sent to the hospital, in hopes of survival.

But he was declared dead-on-arrival.

His father grieved so much for his loss for days. He couldn't forgive himself for his son's death. He felt very lonely without his precious son.

So, he decided to name the animatronic Herobrine gave him as a birthday gift, to his creator.

One day, the man encountered the killer.

The killer tried to slaughter him, but the man fought back, resulting in the killer's-and he, himself's-death.

Years came, and a man named Steve, was hired as the nightguard in the resto. He was drowned in debt, and he undoubtedly needed money.

It was perfectly fine, until on one time, he started seeing flashbacks of the events. (represented by the 'It's Me' hallucination.)

As he was looking around the cameras, he noticed a writing on the East Hall, labeled 'It's Me'.

He also saw a Blaze in the E. Hall Corner at times.

He was terrifed of the flashbacks he was seeing, especially when he remembered Herobrine:

He was the killer's son, the one who helped him kill the poor boy.

Little did he know that Herobrine's angry, restless soul possessed Zombrine and Herobrine the Animatronic.

(This can explain the 'It's Me' on Zombrine's sign, the hallucination, and the piano tune of Herobrine's music box. It was also the reason why the animatronics' eyes were white.)

All these flashbacks became more vivid, until one time, he saw an Enderman, representing Herobrine's soul.

(Endermen were believed to be the souls of children who had very unlucky, untimely deaths. This could also explain the 1/9/8/7 mode in Custom Night.)

He passed the week, unharmed, and he was able to get a notice of termination.

The reasons were:

Tampering with the animatronics. General unprofessionalism. Odor.

The first reason could be because Steve was the one who dismantled the animatronic and remantled it, with the child inside it.

The second could refer to the remantling of the animatronic, primarily because the head can be removed very easily.

(Explains the West Hall Corner's poster where Herobrine takes his head off, exposing his endoskeleton.)

The last could be because Herobrine knew that Steve was the killer's son, the word referring to Herobrine 'smelling' his own blood in Steve's hands.

So, that's all that I have for the theory, and thanks for reading!