Just want to put a little note here that the information used in most of the stories that Mikael is telling Rhaella are from A Wiki of Ice and Fire and the GOT Wikia, that is where I got the information and also this is going to be a long one so sit back and enjoy.
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Rhaella now nine years old-stood at her mother's bedside as she gave birth to what would be Rhaella's third younger brother, Rhaella smiled hearing the cries of her new baby brother after they got him cleaned up and wrapped in a blanket.

Rhaella looks at her father "can I hold him?"

Mikael smiled at her "of course you can little dragon" She walk towards her father who handed her the baby and she smiled down at him "he's so tiny" then she looks at her father again "what's his name father?"

"Niklaus, his name is Niklaus."

Rhaella smiles "Hello Niklaus, I'm gonna call you Nik, I'm your big sister Rhaella and just like with Finn and Eli I am going to be the best big sister ever."

Rhaella kissed her brother's small forehead as Mikael smiled at her "now little dragon why don't you give Niklaus back to your mother and go round up your brothers so they can meet the newest addition to the family?"

She nodded her head "of course father" then she gave her new baby brother to their mother before running out of the hut in search of her other two younger brothers.

She smiles seeing them "Finn, Eli come and meet Niklaus our new baby brother" she took both of their hands and led them into the hut so they could meet their little brother.

Rhaella has been training with her father every day for the past two years and her skills have improved greatly she can now perfectly perform certain attacks and defenses and others are still being perfected with her everyday practices.

After practice, one-day Rhaella looked up at her father "father can I ask you a question?"

He smiled down at her her "of course little dragon what is it?"

She is looking up at him "Why do you call me little dragon? When Finn, Eli, and even baby Nik don't have nicknames like that?"

Mikael crouches down to her level with a smile "come little dragon, and I will tell you a story that will explain why I call you by that particular name" he stands up and leads her over to some logs on the ground and Rhaella sits with her father beside her. "This story will also tell you how you got your name"

The young blonde smiled nodding excitedly happy to finally know why she was the only one with a nickname from her father. He smiled at her "but first I'm going to tell you how it all started"

Rhaella nodded "okay father"

And so he started the story that would answer the young Rhaella's questions "It all started one day in a land far away from here a land called Valyria, and in that land is where the dragons lived, alongside the brave people who rode them. In that time dragons and men lived together in harmony and they did so for many years, The Valyrians, they had a connection to the dragons that others could never understand."

Rhaella looked at him in awe "Real dragons?"

He smiled at her "yes real dragons" then he continued on with his story "But the people of Valyria could not imagine what would happen, what would one day become of their home so they lived on ignorant of the destruction that the future held for them except for one a little maiden, she knew what was to come, you see she had magic in her blood and one night she had a strange dream, that filled her with terror, that little maiden saw the destruction of her home and country, by the raging flames of fire that was near when she awoke she ran straight to her father to warn him of what she saw and by the fear expressed on her face he had no choice but to believe her, and to prepare himself for what was to come. Aenar Targaryen was his name the father of little Daenys, he sold everything they owned and he took his family and their five dragons to live on an island close to a foreign country. And 12 years later, the dream that little Daenys had that night came true and Valyria was lost in a sea of lava and fire, nothing left but smoke and ashes. That event was known as The Doom of Valyria"

Rhaella looks at him "so because of the little girl's dream they survived? What was the name of the place they moved to?"

"Precisely little dragon, the island was called Dragonstone, it was a bleak island citadel beneath the Dragonmont, a smoking mountain in the narrow sea."

Mikael smiled at the awestruck on Rhaella's face "it's getting late little dragon why don't you go and gather your brothers for supper and I'll tell you more of the story tomorrow after your training?"

She smiled "of course father" then she got up from the log and ran to find Finn and Eli already knowing that Nik would be with their mother already with him only being a few weeks old.

Later that night Finn looked to his older sister "Ella will you tell us a story?"

She smiled at him "of course I will Finn" then she took a seat between their beds and is a voice loud enough for the two of them to hear but not loud enough to bother their parents Rhaella began the very story that Mikael had told her earlier that day.

Elijah had fallen asleep during the story but Finn was still awake when she stopped "what happened next?"

The eldest sibling smiled at him "I don't know yet Finn, but I'll tell you tomorrow night when I know the next part... now you should get some sleep, goodnight little brother"

The eight-year-old smiled at her "Goodnight Ella, I love you" Rhaella kissed him on the forehead "I love you too little brother" Rhaella then went back to her own bed on the other side of the room, laying down and falling asleep rather quickly with a smile on her face.

The next day after her training was finished for the day Rhaella looked at her father "what happened next in the story you started yesterday?"

Mikael smiled at her "very well little dragon" Rhaella sits cross-legged on the ground in front of her father ready to hear the story "Now continuing where we left off yesterday. The Targaryens were far from the most powerful of the dragon-lords, and their rivals in Valyria saw their flight as an act of cowardice. However, because Aenar had moved his family away from Valyria, the Targaryens were the only dragon-lords to survive the Doom in 102 BC and the following Century of Blood and Aenar ruled as Lord of Dragonstone until his death, after which his son Gaemon inherited the rule, and so Dragonstone was ruled by the Targaryen's for generations until Aegon I Targaryen who was Lord of Dragonstone until what was to be known as The Conquest, where he conquered Six of the Seven Kingdoms of Westeros... Aegon was also known as Aegon the Conqueror and Aegon the Dragon. So The Conquest is what changed everything for the Targaryens, as the Century of Blood came to an end, the interest Aegon had in Westeros grew. He visited the Citadel of Oldtown and the Arbor in the Kingdom of the Reach with his elder sister Visenya, and he might also have visited Lannisport in the Kingdom of the Rock. He had a huge wooden table made, cut in the shape of Westeros with a map of the seven kingdoms of Westeros painted upon the surface. No borders were painted upon the Painted Table, however, as Aegon believed it should be one realm instead of seven."

Rhaella looks at him "So Aegon wanted to unite the Seven Kingdoms and rule them as one?"

Mikael nods at her "That is correct little dragon, continuing with the story. Argilac Durrandon, who was The Storm King, he reached out to Aegon, proposing a marriage between Aegon and his only daughter, Princess Argella. All the lands east of the Gods Eye from the Trident to the Blackwater Rush were offered as her dowry, although the lands did not belong to Argilac. His offer was an attempt to create a buffer between his own kingdom and that of Harren Hoare, King of the Isles and the Rivers. Aegon spurned the offer, stating he had no need of a third wife, and instead offered his close friend and rumored bastard half-brother, Orys Baratheon, as Argella's husband instead, in return for lands. Insulted, Argilac cut off the hands of Aegon's envoy and sent those back to Dragonstone, upon which Aegon called his councilors together. After six days of consulting, Aegon sent forth ravens to every lord in Westeros, declaring his claim to the throne."

Rhaella looks at him confused "He had two wives?"

"Yes Rhaella he had two wives Visenya and Rhaenys, they were also his sisters, they became known as his sister-wives as well as his Queens" Rhaella looked up at him with an innocent look on her face "but why did he marry his sisters? Why both of them and not just one?"

Mikael chuckled at her questions "Well little dragon the members of House Targaryen, like their ancestors of the Valyrian Freehold, often married brother to sister to keep their bloodline pure, in order to control the dragons and keep their Valyrian legacy. Now with that being said not all Targaryens did this but the majority of them did but they were betrothed from a very young age so they didn't have much of choice in the matter"

Rhaella nodded still not completely understanding but she just went along with it so her father could continue the story "okay, so he was betrothed to both of his sisters? And what happened next in the story?"

Mikael shook his head "No little dragon he was only betrothed to his older sister Visenya but he chose to marry his younger sister Rhaenys as well, his decision to wed them both we nobody really knows why he chose them both" Mikael continued where he left off "So Aegon landed with his army on the eastern coast of Westeros at the mouth of the Blackwater Rush, where he constructed the wooden Aegonfort. Houses Rosby and Stokeworth surrendered to his sisters quickly, and Houses Darklyn and Mooton were quickly defeated in Aegon's first test. Before defeated lords gathered to the new Aegonfort, Aegon was crowned with a Valyrian steel circlet by Visenya and hailed as King of All Westeros by Rhaenys. He also displayed the three-headed dragon symbol of House Targaryen for the first time."

"A three-headed dragon? That's so beautiful"

The older man smiled at his daughter's excitement "Would you like to see the sigil for yourself?"

Rhaella looked at him wide-eyed "How?"

Mikael smiled at her again "Sit right here and I will be back, in just a moment and I'll show you how"

Rhaella squealed excitedly "okay father"

Mikael walks off towards the hut to retrieve Visenya's sword to show little Rhaella the Targaryen sigil. After he has the sword in hand he returns to his place in front of Rhaella he shows her the sheath of the sword "see that's the three-headed dragon."

She grins "That is incredible father... I was right it's beautiful."

He smiled at her again "I will explain about the sword once this story is complete"

Rhaella nods "okay father"

He picks up the story once again right where he left off "The Targaryen siblings departed the Aegonfort, with Aegon marching northwest into the Riverlands to confront Harren Hoare. Edmyn Tully, Lord of Riverrun, declared for Aegon and led the Riverlords in revolt against the ruling ironborn. When Harren refused to yield Harrenhal, Aegon attacked the gigantic new castle with his dragon Balerion, and House Hoare was extinguished with the burning of Harrenhal. The next day Aegon named Edmyn as Lord Paramount of the Trident. Meanwhile, Rhaenys and Orys defeated the Durrandons in the Last Storm, while Visenya fought the Arryns and secured Crackclaw Point. After regathering at Stoney Sept, the Targaryen siblings advanced against the larger host of the Two Kings. The Targaryen dragons, Balerion, Meraxes, and Vhagar allowed Aegon to achieve a great victory at the Field of Fire, which resulted in the death of Mern IX Gardener, King of the Reach, and the surrender of Loren I Lannister, King of the Rock. Aegon then marched for Highgarden, where he named Harlan Tyrell as Lord Paramount of the Mander after the castle's surrender. The Targaryens again reunited to face the host of Torrhen Stark, King in the North, but Torrhen chose to kneel to Aegon along the Trident instead of fighting a battle.

Visenya returned to the Vale, where she achieved the surrender of the Arryns with no bloodshed as the young King of The Vale, Ronnel Arryn was entranced by Vhagar and so Visenya brought the Vale of Arryn into her brother's realm, while Rhaenys flew to Dorne in an unsuccessful mission to the Martells. Aegon, meanwhile, marched to Oldtown, which was surrendered to him by Lord Manfred Hightower upon the advice of the High Septon. Within the Starry Sept, the High Septon declared Aegon to be King of the Andals, the Rhoynar, and the First Men, Lord of the Seven Kingdoms, and Protector of the Realm."

Rhaella looked at her father still in awe of what she's just heard "So Aegon became the first ruler of the Seven Kingdoms?"

"He did but Aegon chose to date the beginning of his reign from the day the High Septon anointed him in Oldtown. Rather than ruling from Oldtown or Dragonstone, Aegon chose to make his seat King's Landing, the new settlement growing around the Aegonfort. He also took the swords of his defeated enemies, forging them into the Iron Throne with Dragonfire breathed from his dragon Balerion. Aegon also began what would become known as the small council, as well as that of the Hand of the King, with Lord Orys Baratheon becoming his first Hand. Aegon's first established law was the King's Peace, which forbade conflict in the realm without the leave of the Iron Throne. Aegon treated the defeated lords with respect and allowed each region to retain its own laws and customs and for the lords to retain both the right of pit and gallows and the first night. Aegon often traveled the realm with six maesters who educated him on each region's local customs and history.

During Aegon's Conquest, the lords of the Three Sisters had declared their independence and crowned Lady Marla Sunderland as their queen. Following his coronation at Oldtown, King Aegon commanded Lord Torrhen Stark, the new Warden of the North, to end the rebellion, and he sent Queen Visenya Targaryen on Vhagar to accompany the northern army led by Ser Warrick Manderly. At the sight of them, the Sistermen abandoned their queen and installed her younger brother, Steffon, as their new lord. Steffon soon bent the knee, swore his fealty to House Arryn, and re-entered the King's Peace, ending the rebellion of the Sistermen's Rebellion.

In 2 AC, Aegon turned his attention to the Iron Islands, where the ironborn had been fighting for two years over the kingship. Aegon landed on Great Wyk with Balerion and a war fleet to deal with the contenders. Aegon personally cut down Qhorin Volmark with Blackfyre, while the priest-king Lodos walked into the sea, drowning himself. The other contenders quickly bent the knee. Aegon ignored the suggestions of making the ironborn vassals to the Tullys of Riverrun or the Lannisters of Casterly Rock, as well as the suggestion to exterminate the ironborn by dragonflame. Instead, Aegon allowed the ironborn to name their own lord paramount, for which the ironborn chose Vickon Greyjoy as Lord of the Iron Islands."

Rhaella sat there taking it all in with an awestruck look on her face as her father continues "Now for the final part of this story and tomorrow, I will get to the story that answers your questions little dragon." So he continued and told about The First Dornish War, and to bring the story to a close he told her of the end of Aegon's rule and his legacy.

Rhaella looked at her father in awe once again "what about the sword you said you would tell me about it at the end of the story"

He held it up for her to see "This sword belonged to Visenya, which is why the Targaryen sigil is engraved onto the sheath, its name is Dark Sister and it was used to protect Aegon by his sister, with Visenya's death the sword was said to be lost over time and after tomorrow's story I will tell you how it ended up in my possession"

Rhaella smiled happily "okay father" then she ran off to help her mother prepare supper as she was told to do by her father. That night at bedtime she once again sat between Elijah and Finn's beds and she told them the rest of the story that was told to her by their father. Mikael smiled standing in the doorway watching as his little dragon turned his story into a bedtime story for her younger brothers. Rhaella noticed that halfway through the story that both her younger brothers were sleeping she smiled kissing both of their foreheads and heading off to her own bed.