Upon his birth, the younger twin was named Daemon II, in honor to his uncle. He was given a green egg which later hatched the dragon Meraxion.
Daemon usually follows and even copy everything Aemond does, taking him as the greatest example. Yet, they have quite unique personalities, with Daemon prefering to focus on studying the other realms and their languages. He is very good with people, cunning and charming, using these traits at his will.
Daemon and Aemond are two halfs of a whole, one completes the other.
When they were 10, the siblings were flying above the Red Keep, Rhaenyra with Syrax, Aegon with Sunfyre and Helaena with Dreamfyre and Aemond with her. Exchanging looks with his twin, Daemon mocks about Syrax appearence, which anger Rhaenyra and makes Syrax attack Meraxion, who gets heavily injuried and falls during the fight, almost killing his rider.
After the death of his dragon, Daemon nuture nothing but hate for his half-sister and her dragon.
Daemon grow his teenage years without a dragon, having studied diplomacy to keep his mind sane, but his greatest wish was to be able fly out alongside his brother. As the years passed, vain comparision between him and Aemond started to anger the prince. When once they were identical, now Aemond was taken as the fearless one, while Daemond was some sort of prince charming, despite having all the good qualities of a great warrior.
Daemon's life take a turn when his twin return from Storm's End with the news of the death of Lucerys. He knows a war is inevitable now and they will lose, because Vhagar and Sunfyre alone cannot win it.
In a bold and desperate move, Daemon infiltrates Dragonstone, ready to die or to claim a dragon. His wit was enough to make Vermithor accept him as his rider, and before the blacks could notice, the prince stole the dragon, counting with his twin and Vhagar's protection as they left Dragonstone.    Black council verse
(The incident on which Meraxion was killed never happened)
When Daemon realized the thorough search for Aegon after their father's passing, he knew they were going to crown him over their half-sister.
He then gather with Sor Erryk, handing Viserys crown and giving him instructions to wait for him at the Pit. As Aegon's coronation begin, he remain at the castle and rescued princess Rhaenys from her quarters, leading them to the Dragon pit. As they escaped, Daemon took Meraxion, while Rhaenys carried Sor Erryk on Meleys.
Upon arrival at Dragonstone, Daemon swore loyalty to Rhaenyra, knowledging her as the true Queen. But, despite the honesty, he was kept under surveilance for a while, which he didn't complain, considering the public knowledge of his love for the family.
Months pass of his arrival to Dragonstone, the battle of Rook's Rest happens and with Aegon gone, Daemon fear for the safety of Helaena. He begs for Rhaenyra to allow him to rescue both her and Jaehaera*. After getting the Queen's permission, he informs Helaena through her handmaiden, and rush to King's Landing. They manage to escape the castle and while Daemon kept Aemond's attention on himself, flying above the Red Keep, Helaena manage to enter the Dragon pit and retrieve Dreamfyre.
As Aemond left the keep to get Vhagar, Sor Criston Cole gave the order to put down Meraxion, and despite the dragon's speed, he gets hit by a scorpion, the spear piercing through his chest and even wounding Daemon. Helaena manage to maneuver Dreamfyre to prevent Daemon from falling, but his dragon is lost.
Daemon is wrecked with the loss of Meraxion, but Helaena and Jaehaera are safe, so it was worth.
Only a week later, Rhaenyra asks a huge sacrifice of him: to try claiming Vermithor. On which he fails, ending with the death of many Dragon Guardians and almost his own. His bond with Meraxion was still too strong and grief was too recent, leading Vermithor to deny him.
A week later, when his grief had become rage towards Aemond not having stopped Meraxion from being shot, he sneak into the dragon pit, yelling at Vermithor that he should either become his rider or perish by his fire. And this time, Vermithor accepted him, ackowledging the fire burning in Daemon's heart.*we can plot if blood and cheese happened or not, given I doubt Helaena would feel safe in Dragonstone if it did.