In the Underworld, Familiar forest

From a distance you would believe that it was an ordinary forest, with ordinary trees and ordinary animals. If you were to get closer however you would notice that all the living organisms aren't what you'd call natural. In the centre of a forest there is an immense mountain with a large cave at the base, where two glowing golden eyes can be seen glaring out over the expanse of woodland that this mighty creature calls home.

"Soon" it thought "Soon I will meet a devil worthy to be my master and I their familiar"

After which it let out a tremendous roar that shook the entirety of the forest. Then closed it's eyes to wait.

Three days later

"I just know I'm going to find it" shouted the young girl that sat on the head of a red scaled reptile like creature.

"Settle down Rias, choosing your familiar is very important to becoming a high class devil" said the crimson haired satan. This happened to be Sirzechs lucifer the current head of the devils and the king of the underworld. with him he has his younger sister Rias, his mother and father, Lady and Lord Gremory and his queen Grayfia lucifuge, the silver haired queen of annihilation.

With them was also the familiar master, Zatuji, who carried with him a book of all the possible familiars.

"So Rias what were you thinking of your familiar being like?" asked her brother with a gentle smile on his face.

"I want one that's very powerful and that can scare Riser-baka," It was common knowledge throughout the underworld of the young heiress' displeasure towards her future fiancé. "I also want it to be the same colour as my hair," she exclaimed whilst showing the others a lock of her crimson coloured hair.

"I am afraid there is nothing in this book that matches your requirements my dear," said Zatuji.

The others looked pityingly towards the now pouting girl.

"But he said there is a creature in this forest that matches your description, but I'm afraid you can't make it your familiar."

"Why not?" she sulked now once again pouting.

The others were also very confused as Zatuji had been known to support anyone's decision on familiar.

"That's because it is the largest dragon I have ever seen," he explained, "he arrived in the underworld 60 years ago and would hunt down any strong opponents it could find. Others have tried to make him their familiar but all were sent away by a large stream of fire even Riser Phenex tried and failed so ended up with a fire eagle.

This however only made Rias more excited at the prospect of having something that Riser couldn't have. "Now I am definitely going to get it so I can finally be rid of that baka," however whatever she was going to say was cut off as she was plucked off her standing position on the lizard and was carried off by a large eagle.

"Rias-chan!" exclaimed the satan in panic, "We have to catch her he shouted to the others while spreading his wings.

"Yes Sirzechs-sama came the instant reply.

With Rias

Rias kept screaming hoping that someone would come an save her. As they got closer to the mountain she noticed a nest and screeching noises coming from within. To her horror she realised that she was going to be eaten alive. This sudden realisation caused her to start crying harder.

Suddenly there was a tremendous roar which caused the eagle to start panicking. Rias turned around and gasped at what she saw. Barrelling towards them was an enormous dragon. It was covered in glinting red scales with a tan under-belly, it had a triangular head with a large horn at the end of it's snout.

It let out another ear splitting roar and covered the distance between them in a matter of seconds. It then lunged at the eagle grapping it in it's large paw.

The bird tried to fight back but the dragon just squeezed it's paw causing the bird to cry out in pain while also releasing the young girl in it's talons.

Rias screamed out in shock as she fell, whilst on the ground the Satan had opened his wings ready to catch her. But as they did this the dragon dived down and caught young Rias in his paw while gently lowering itself to the ground. All the while thinking "I have finally found it, I have found the one that will free me from this curse of perpetual loneliness," Back on the ground Rias launched herself into her brother's arms, who after noticing the large gashes on her arms quickly activated a healing spell.

After Rias had calmed down he turned to the dragon who during all of this had quickly shrunk down to an average sized dragon. The others who had just caught up gasped in shock after witnessing this.

Sirzechs turned towards the dragon and said "Thank you for saving her," The dragon nods it's head in understanding.

"This is incredible a large dragon showing kindness to a young devil, this has never been seen before," exclaimed Zatuji

"Quickly Rias" Sirzechs whispered in her ear "try and make him your familiar,"

"Hey Mr dragon would you like to be my familiar" she questioned. The dragon raised it's head and looked to be in consideration before bending down and blew hot air at Rias knocking her onto her backside. "Hey!" she whined "Do you want to be my familiar or not?"

The dragon then bowed it's head to her as a sign of acceptance. Rias giggled in glee.

"I Rias Gremory here by summon you to be my familiar to help me your master in what ever I may need." Then a giant crimson magic circle appeared underneath the dragon with it in the centre.

"Grayfia darling could you organise a party for when we get back please?" said Venelana

"Yes of course"

"But why mother?" asked Rias

"Because my dear when news gets out that you have a dragon as a familiar all the newspaper will go mad in trying to find out how you managed to get a dragon to be your familiar."
After turning back to the dragon, Rias exclaimed, "I'm going to call you Natsu"
The others sweat dropped at this as it was such a childish name for such a powerful dragon, but to a 10 year old Rias she didn't care as she had finally found her familiar, one that would soon strike fear into the hearts of anyone who would be stupid enough to go against them.
'Natsu' then bent down in a way that showed he wanted her to get on.
"Oh no you don't Rias," her mother shouted with panic and worry setting in to her voice while lunging forward to stop her.
Rias replied by sticking her tongue out at her as she dodged out of the way of her mother's hand.

Natsu as Rias got closer angled his leg to allow her to climb on easier. She jumped on and positioned herself in a comfortable spot and signalled to Natsu to take off. Then he spread his massive wingspan and took off, blowing away the surrounding trees. The others watching from the ground could only smile as they listened to Rias' giggles of joy as they tried to keep up with the dragon.

Rias then lied on her back and stroked Natsu's glistening crimson scales as they soared through the sky and smiled. Unknown to everyone else, Natsu as well was smiling.

At the Gremory mansion.

When everyone had arrived, Natsu slowed down to come in for a landing in the Gremory's large garden. As he landed the earth shook a little then he lowered himself to allow Rias to get off.

When everyone got ready to go inside Sirzechs told Natsu, "I'm afraid you can't come in as you are too big to fit inside."Rias turned back around and flung her arms around Natsu's head and whispered, "Good night Natsu, I will see you in the morning." Once they had all left Natsu shrunk down and lowered himself to the ground, resting his head on his paws he shut his eyes and went to sleep.