I was so excited to see a good portion of y'all wanted to see my double headcanon for Blueblood and Thorax, so here we go!
Duke Blueblood
Born to a wealthy unicorn couple distantly related to the royal family, Blueblood had everything handed to him on a silver platter. With Celestia and Luna as his great aunts and Cadance as his cousin, it was normal for him to almost be raised in the Canterlot Castle by his governesses and tutors. He rarely saw his parents, except for grand occasions at the castle, and often felt lonely even in the constant company of servants and guards.
Blueblood’s parents, Posh Patrician and Debutante, “raised” their only child to care for the finer things. They were sure to make polite conversation with their son whenever they saw him at extravagant Canterlot events, but their talks rarely lasted longer than a minute or two. Even with their noncommittal attitude towards Blueblood, they made sure to drill a few rules into his head though his governesses: everyone wants something from you, true love is for morons, you must outsmart everyone around you, and relationships or marriage have to be for advantage. They also made it very clear that non-heterosexual, non-cisgender, and non-pony creatures were absolutely abhorrent and filthy, and didn’t make it unknown of their strong opinions.
Like a good portion of his family, Blueblood received his cutie mark in leadership. The compass needles on his flank represent his skilled ability to help send ponies on the path to success and well-being, but he seemed to lose his own way shortly after getting his cutie mark. He seemed to have no interest in helping other people when he felt so lost.
Being a part of a high status, Blueblood had only the best when it came to education, housing, and anything else his heart desired. He was very popular among students while he was attending Celestia’s School for Gifted Unicorns and regularly had young mares confessing their love to him every other week. He rejected them all swiftly, remembering what his elders had taught him. After all, these mares didn’t know anything about him, they just cared about his family’s wealth and power. Blueblood felt no real connection to the mares who threw themselves at him and avoided them unless he absolutely had to bring someone to an event and make a good show in front of his parents.
By the time Blueblood was an adult, he had seemed to become a callous and skeptical pony, just like his parents. He believed anyone who tried to get close to him just wanted something from him and trying to meet mares didn’t help. His parents regularly tried to set him up with other wealthy and high-born mares, which he feigned enjoyment with only when eyes were on him. But when he was alone, he couldn’t seem to resist staring at the male guards in the castle.
The night Blueblood met Rarity was the night he snapped. It wasn’t uncommon for mares to approach him at galas, but Rarity’s strong attempts to have the two be an instant match was enough to set him off. He decided that if she was so convinced that he was the one, he would act like the biggest jerk in the world. He made sure to put himself first, making her put down her own shawl in a muddy area and slamming doors in her face all throughout the night. And when she called him out at the end of the event, he had never felt more accomplished. Blueblood was positive that Rarity would never try to be with him again.
After awhile (and after hearing about his behavior at the Grand Galloping Gala), his parents started to question him on when a mare would be good enough for him and when he would decide to choose another high-born to marry. He pretended as though he was simply following the rules of his parents and working to outsmart everyone else around him to work a mare to his advantage for marriage, and his claims seemed to subside them temporarily.