10 year old Regulus Black was a sullen boy. He held much resentment in his heart. Most of it, directed to his mother, Walburga. It went without saying, of course, that a portion of that hatred was directed at his older brother, Sirius, Walburga's golden boy, heir to the Noble and Most Ancient House of Black. Sirius was treated like a king, and he looked like one too. Even at a young age, the aristocratic and attractive features that defined the Black family was evident on the older boy's face. He had a casual elegance to him, from his curly, shoulder-length black hair down to his toes. He was often dressed regally, in the finest materials that money could buy. His eyes, unlike the rest of the family's, were silver-grey and framed by long, dark eyelashes.
Their mother and father took him to parties, sent him on playdates with children of other respectable pure-blood families and let him do whatever he wanted. Regulus, on the other hand, practically didn't exist. He couldn't remember the last time Mother had let him out of the dingy old house they lived in. The only people he ever met were close family members who came by often to have dinner at Grimmauld Place.
That was another thing Regulus was sulky about. Mother had drummed into him and Sirius that they heralded from the most powerful and richest pure-blood family to ever exist. Often, Mother went on and on about how the Black family could trace its genealogy back centuries and how every single person in that family was of pure blood. She'd told them that to be Black meant that they were practically royals, and that Sirius was the next King. And yet, they lived in this oversized, moth eaten townhouse, tucked away between a row of Muggle townhouses. If they were royalty, surely they deserved a palace.
Sirius had mentioned to him before that the paterfamilias of House Black, their grandfather Arcturus Black III, lived in a huge manor somewhere in Scotland, and that their land flowed over the hills and glen. Regulus had never been there before - Mother hadn't thought him important enough to introduce to the Head of the family, unlike Sirius who went there every year for the Black Family's traditional Yuletide Ball.
But if there was something that Regulus was most envious about, it was James Potter. James Fleamont Potter, son of Fleamont and Euphemia Potter was their second cousin, once removed on Mother's side and twice removed on Father's. Their great-aunt Dorea had married Fleamont's older brother, Charlus, and since the Potters were pure-blood, she hadn't been blasted off the family tree. Regulus remembers the very day when Dorea came to visit the family at Grimmauld Place - the first time she mentioned that she had a nephew the same age as Sirius. Regulus didn't know then, but that was the very day that led them down this slippery road. He didn't know that the simple suggestion by their kind grand-aunt would lead to him losing his brother.
It'd been almost 3 years now, that Sirius and James had been best friends. Regulus could remember when it used to be Sirius and him against the world, brothers and best friends forever. Now it was Sirius and James, and Regulus was left alone at home with only Kreacher to entertain him. Sirius wasn't unkind to him - much to the contrary, Sirius was still close to him and was still very much a great brother. But Regulus didn't have any friends, and he couldn't help but feel jealous of his brother and his adventures at the Potter estate.
It didn't help that Sirius was 11 this year, and so was James, which meant that they'd be off to Hogwarts come September. Now, Regulus wouldn't even have a brother who'd sneak into his room every night and tell him stories of the old manor houses and lush gardens that he visited with Mother and Father as the Heir Black.
Everything changed on 2nd September 1971. Mother had been awaiting Sirius' owl about his first day at Hogwarts. She had been bragging and boasting about how the Heir Black would have the entire Slytherin House under their thumb, how he'd be royalty there too, especially since he'd been paraded around previously. Every pure-blood child grew up knowing of Sirius Orion Black, heir to the Noble and Most Ancient House of Black. But Regulus' shock when he heard his mother's strangled scream upon seeing the letter was nowhere near close to what he felt when he heard that his brother had been sorted into Gryffindor.
Sirius Black, son of a long line of pure-blood Slytherins, heir to a family that was as dark as they came, was in Gryffindor House. Oh the shame.
Mother cried for hours before she worked up the strength to send her son a Howler describing how he was a shame to the family name and that she knew she shouldn't have let him befriend that Potter boy. She spat the word out like it disgusted her, and if Regulus was being honest, it probably did.
Of course, in hindsight, Regulus wasn't even sure why he was shocked. Behind his brother's perfect life, there was a side that was hidden to everyone, even family. Sirius was light in a sea of darkness. He had never agreed with mother's views on blood purity and was extremely vocal about it. Regulus couldn't count the number of times Sirius came into his room with a slight limp or a split lip after one of Mother's numerous house parties. Regulus was never allowed to attend, but he'd hear everything about it from Sirius. His brother never told him about his arguments with Mother, but Regulus could hear every spiteful word and every painful blow that came from the kitchens below.
To the outside world, Sirius was the perfect pure-blood heir, but Regulus knew that Sirius hated it. He hated their family ideals and beliefs. He hated their cousin Bellatrix, who would never stop talking about the Dark Lord and how he was the perfect champion for blood purity. But most of all, he hated their mother, who had hexed and jinxed and even physically hit him for as long as he could remember, simply because he didn't think that Muggles were all that bad.
And so, it was on 3rd September 1971, that for the first time in a long while, Walburga Black turned her eyes to her younger son, dressed him in the finest silk robes and presented him to Arcturus Black III. That day marked the beginning of a year long effort by Mother to showcase Regulus as the new Heir Black. Everywhere he went, he was constantly reminded of how much he looked like Sirius, except the eyes - he had the traditional Black family eyes, dark and brooding. Personally, Regulus thought that Sirius had a certain elegance to him that probably came from being the firstborn, something that Regulus would never have. He was invited to parties and balls and received long lectures from his mother about the importance of blood purity. Regulus had never met a muggle or muggle-born before, so he honestly had no opinions on the matter. But Regulus had seen what had become of Sirius, and he would've much rather shut his mouth and nod his head at everything Mother said, than be forced to endure the beatings and abuse that Sirius did.
When Sirius returned in the summer of 1972, he was treated with disdain. Locked in his room half the time, beaten whenever he said anything out of line, Sirius left Grimmauld Place a whole month before the new school year started. He didn't say where he was going, but Regulus knew that he'd be with James Potter, his best friend and fellow Gryffindor. Whilst he was home though, Sirius tried to be a good brother. He constantly tried to sneak into Regulus' room to tell him stories of Hogwarts and his adventures with all his friends. He was hurt that his brother never replied any of his letters, but Regulus' sad face told him that the younger boy hadn't even received them. Mother had torn any letter that Regulus received from his brother, refusing to allow their last hope for a perfect heir to be sullied by Sirius' muggle-loving tendencies. Their mother soon found out about Sirius' night time trips to Regulus' room and the punishment that followed left the older boy unable to move for a whole day. Their father had taken pity on Sirius and healed most of his more serious injuries. The next day, Sirius was gone.
With that, Regulus Arcturus Black became the perfect heir that Walburga had always wanted. After the holidays, his parents had sent him to Platform 9 ¾ and had even settled him down in a carriage occupied by a few older Slytherin students, including his cousin Narcissa and her betrothed, Lucius Malfoy. Much to Mother's delight, he was even sorted into Slytherin House and had befriended several children that were heirs to other pure-blood families that were predominantly Slytherin.
Regulus had thought that being at Hogwarts with his brother would finally allow them to interact without the threat of punishment from their mother. But nothing could have prepared Regulus for the great rivalry between his and his brother's Houses. He had always known that Slytherins and Gryffindors generally hated each other. Sirius never personally did anything to him, no one did. But the animosity between the houses made it impossible for them to communicate without becoming social pariahs. And Regulus soon found out that one wrong move and a sneaky snitch from Slytherin House will go tattling to their mothers about how the perfect Regulus Black was fraternising with the enemy. The rumours would reach his mother's ears and he would receive a strongly worded letter and a promise of punishment the next time they met.
So, Regulus went along, trying his very best to enjoy life at Hogwarts. He soon made some friends whom he genuinely liked and whom Mother approved, and he began playing Quidditch, which he found himself enjoying immensely. His talents as a seeker did not go unnoticed, especially by his Potions teacher Horace Slughorn. Regulus was soon inducted into the prestigious 'Slug Club'. Created by Professor Slughorn, it was an elite club of students that he handpicked, identifying them as those he potentially thought would have an outstanding future in various fields. Regulus had been selected because of his talents as a seeker as well as the fact that he was heir to the extremely important House of Black. His life continued fairly normally since then, and whilst he did not feel particularly strongly about the whole blood purity situation, he still wasn't inclined to make himself a social outcast, so he went along with what his family and friends preached to him.