Once upon a time, there were two demons. One, an ancient and highly skilled demon butler. The other, a clumsy, thirteen year old human-turned- demon, who was pretty close to utterly useless.
But this isn't really a fairy tail, so it should probably start differently. Maybe with something like... Oh I don't know, so I'll just throw you right into the middle of it, like so.

It was a month after Ciel had become a demon and had left England with Sebastian forever bound as his servant.
On one rather overcast afternoon, Ciel and Sebastian were walking down a path through the forest when they were attacked by a very powerful wizard, who called himself Eric. A name which Cile found all together too common.
"Sebastian," Ciel said in a bored voice, "I order you to kill that wizard."
"Yes, Young Master." Sebastian smirked and ran toward the wizard.
They fought for a few minutes before the wizard cast his most powerful spell on Sebastian.
Due to a very shameful mistake, the spell hit Sebastian, and he fell down and fainted.
"Sebastian!" yelled Ciel. Sebastian had never been defeated before, and he had never not been able to carry out his master's orders. Ciel wasn't entirely sure how to deal with this, so he did the most sensible thing he could think of.
He dragged Sebastian away (None to gently, I might add.) and luckily, the wizard let them go, too busy laughing at his own amazing abilities to notice them leave.

When at last Sebastian woke up and opened his eyes, he turned into a horse.
Ciel screamed and scuttled backward in shock. He was so surprised at Sebastian being a horse, that he then proceeded to feint.
"Neigh!" Sebastian neighed. He galloped to the nearest cliff, which just so happened to be a few feet away and not very high (just high enough to kill a human) and because he was so unhappy at his inability to obey his master, he leapt off the cliff. Naturally, being a demon, his attempt at suicide failed, and he only managed to knock himself out again.

An hour later, a girl named Ilia found Ciel and Sebastian and took them to her village, Ordon.

"Sebastian and I have been living here for the past six years. I am now seventeen, and Sebastian is still a horse. I suppose his age doesn't matter since he is a demon that is hundreds of thousands of years old.
Oh, wait. I'm a demon too.
Tomorrow is the day of my eighteenth birthday, I hate my birthday, nothing good ever came of my birth or of that day.
And tomorrow will no doubt be the same."

-0-0-0-

"Ciel, don't you ever feel like there are spirits around? It is said that our world and theirs merge at the time of twilight. That is when our worlds are nearest... It's getting late, we should go back to the village now." Rustle stood up and walked down the path that led to Ordon village. Ciel, who had dyed his hair blond and used a blue contact lens to conceal his identity, stood up and followed Rustle into the village.