Saying that Bellatrix and Sirius didn't get along was a huge understatement.
It wasn't that they believed in different ideals, because that was completely untrue, especially in the younger years of Bellatrix's life. She just wasn't brave enough to go against her mother and her family's ideals.
Bellatrix had always admired Andromeda, but it was nothing compared to what she thought about Sirius. She envied him for openly defying his mother's teachings, for standing up for his younger brother when she didn't have the guts to do so for her sisters.
Bellatrix resented him, hated his easy-going attitude at carrying the Black name, and his carefree nature regarding the 'proper mannerisms' they were taught to obey by their families.
She didn't let herself be corrupted by her family's practices at first, but slowly, as her will gave way, the wall inside her protecting her from turning like them slowly crumbled, and bit by bit she forgot all the things she believed in.
Being sorted into Slytherin didn't exactly uplift her morals either—being surrounded by people who supported the Dark side, people like those in her family... it became increasingly difficult for Bellatrix to remind herself of what she believed in and stood for with the passing days.
As the years passed, trouble caused by Bellatrix in school increased, and so did the complaint-letters being sent to her parents. Each time she received a letter back from her parents, it was appreciation for torturing an innocent muggle-born, and she got a sick feeling in the pit of her stomach, one that she had learnt to ignore.
Seventh-year was the turning point in her life. She was branded with the Dark Mark, a tattoo her family wanted her to have since the day she entered this world, but she didn't feel any over-whelming feeling of happiness or relief or gratitude inside of her, as her parents and relatives had assured her she would feel. Instead, it felt like the candle that burned with the hope of redemption inside of her had been extinguished.
The disapproving looks both her sisters had given her left her in tears, though she would never admit that. Sometimes, all she wanted was to feel loved.
As the Death Eater meetings increased, Bellatrix found a purpose in life. She began to found joy in hearing the tortured screams of the prisoners. Her face had acquired a sinister look to it, her eyes had become wide and wild, and sometimes she didn't quite recognise her own self in the mirror anymore.
Thus began her slow descent into madness.
She was soon accepted into The Dark Lord's inner circle, proving herself to be one of his most loyal supporters. Voldemort was dark and commanding, cruel at times too, but he was adored by each and every one sitting on the table, including Bellatrix.
There, she met Rodolphus Lestrange. She knew him from school, obviously, but they hadn't really talked about anything other than schoolwork before. He liked her for all the things that made her, all the things that she felt insecure about.Now her mornings weren't grumpy, but happy because she finally felt loved. She had everything she had ever wanted.
Then Andromeda ran away with that muggle boy. She wasn't supposed to feel anything for her disowned sister, she didn't was to shed tears over... that blood-traitor, but deep down, the old Bellatrix, the one that was reshaped by circumstances, did love her younger sister.
She and Rodolphus got married in an intimate wedding ceremony, and that may have as well been one of the best days of her life, provided Andromeda had shown up, the one person among the crowd who she knew had some compassion in her, who could make Bellatrix see the good in herself. Instead, Andromeda's absence simply reminded her that she was surrounded by completely sadistic people.
As Bellatrix began attending more and more Death Eater meetings, her missions got more and more gruesome, and the secrets she kept became darker and darker, so dark that at times they didn't let her sleep at night.
And then Sirius Black got disowned. Old Bellatrix would have envied him for being free from their family's clutches, but this wasn't Old Bellatrix anymore. She was long gone.
Then Narcissa started seeing Lucuis Malfoy, and while her parents couldn't have been more thrilled, deep, deep down, Bellatrix wanted her sister to lead a life without all this nonsense. But there was nothing she could do to express her feelings to anyone. She could just as easily get disowned, blasted off the family tapestry like Sirius and Andromeda.
Then rumours that there was a boy, a boy born on the last day of July, a boy that was destined to kill the Dark Lord came up, and Voldemort went out to prevent his own death, taking information from a man who was supposed to be the boy's father's best friend. But the baby somehow escaped with but a scar on his forehead.
Sirius was arrested that night, because according to the Ministry, Bellatrix's cousin had given the location of his best friend's house to the Death Eaters, but she wanted to shove Peter Pettigrew in front of the Ministry's faces saying that it was him and not her cousin. But she didn't because she couldn't.
Without a leader, the Death Eaters got more and more careless, and she, along with a few others was arrested for torturing Frank and Alice Longbottom to insanity. She was dragged to Azkaban, but she wasn't scared. She was laughing so hard; shrieks of maniacal laughter that were, what she assumed her own, surprised her. It was at that moment that Bellatrix realized that she had truly lost herself.
She passed Sirius's cell there, and they locked eyes for a second. The bright eyes and sly smile that had always adorned his face before was gone, and this man was unrecognizable to Bellatrix. He sneered at her, and for once, she didn't even care.
She continued onward, her chin high, as though being sentenced to live life with dementors and bad meals didn't bother her. She wanted to look unbothered, undeterred even in imprisonment.
She was kept in a cell with Rodolpus, and first she was happy to have a bright spot in what seemed like a miserable life ahead, but that feeling didn't last long. She and he gradually grew apart, and it was soon impossible to tell that they had once loved each other.
Then, the horrible cold settled in. It came slowly, creeping up her arms and legs until she was full of it, until that was all she knew. Her body became numb to her and the thin clothes they gave her did little to keep her body warm.
She had no sense of time inside that horrible prison; she didn't bother marking the days on the wall. It could have been six months or six years for all she knew.
She stopped reading the newspaper, too, as since Voldemort wasn't in the picture, there was nothing there for her Gossip articles by that horrible wth—Rita Skeeter—did not engage her at all.
Then, after who-knows-how-many years, the day of her escape came. The dementors came, and just opened the door for her and her husband. They stared at each other, stupefied, and burst through the door. Down the corridor they ran, and were soon joined by their other companions.
Outside the prison, stood someone she never thought she'll see again: Lord Voldemort himself.
She wanted to run and put her arms around his neck, whisper how glad she was that he was back, standing right there in front of her. She never thought that she'd ever be this happy ever again, not when the dementors had made her relive all her worst memories, bit by bit.
She kneeled down, and put her right fist on her heart. "Master."
Slowly, all around her, the other Death Eaters followed the same thing. Once Voldemort had allowed them to stand, Bellatrix asked the question swimming in her mind ever since she saw him. "How?"
Voldemort smiled slyly, and responded, "Later, Bella. All will be explained. The Ministry officials will be here soon. Wreck some havoc, now, it has been quite a while since any of you have been allowed a wand... Leave something for them to find."
And so they did. They found their wands in an old shed outside the ocean, and went on a destroying-spree.
The Death Eaters assembled together for the first time in fourteen years a little outside the Hogwarts grounds, the last place anyone would look for them. There, Voldemort took them to the Malfoys' house's basement, and thus began their first meeting in fourteen years.
As Voldemort began giving instructions, Bellatrix admired him, admired that he was sitting right there, in front of her, having risen from the dead. She admired him to have enough magic to make not one horcrux, but six, as he told her after the others had departed. That feeling she had with Rodolphus before Azkaban returned.
That year was all about the stupid Order of the Phoenix. The Death Eaters and Voldemort lured Harry Potter to the Department of Mysteries (Bella had said that Lily and James' son wouldn't be thick-headed enough to fall for that, but she was wrong), and along with him him little gang of friends.
There, Harry Potter had spoken the Dark Lord's name, a name even Bellatrix, his most loyal supported didn't dare to speak. She had completely lost her mind over that and was almost ready to break that glass ball to kill the boy. That little nuisacnce had chased her and the others all around the Department of Mysteries. She was amazed at how five teenagers were able to evade an entire team of Death Eaters for such a long time... surely their skills hadn't become so rusty over the years?
Seeing Neville Longbottom, standing there, ready to fight for his friend, Bella almost laughed out loud. She wanted to torture him enough so that he could join his parents at St. Mungos. The moment this thought appeared, she felt a bit ashamed of herself, but reminded her this is how she ought to be. Her position in this world is right. Her hand moved on its own accord, and before she knew it her tongue had formed the words. "CRUCIO!"
Longbottom writhed on the ground, pain distorting his features, his anguised screams filling up the cavern. She stopped quicker than what was expected of her sand said, "That was just a taster! Now, Potter, either give us the prophecy, or watch your little friend die the hard way!"
Then in came the Order, five people, noticed Bellatrix, which included her sisters daughter, Nymphadora, and Sirius.
Straight away, she went to Nymphadora. She hadn't seen or maintained any form of contact with Andromeda before Azkaban, and doing so in the wizarding prison was completely impossible. Being close to Andromeda's daughter was the closest she had been to her disowned sister since the past twenty-four years.
Nymphadora's hair was pink—definitely a Hufflepuff. What a disgrace, thought Bellatrix, having completely seen her niece. Filthy half-bloods and their fancies.
She effortlessly stunned her niece, and advanced forward, looking for another target. She found one in none other than Sirius.
As they duelled, like they had many years before in the Black House, Sirius shouted, "Come on, you can do better than that!"
Oh, I'll show you how good I can do, she thought. "STUPEFY!"
It seemed like it took a million years for her cousin's body to fall, and once it slipped behind the veil, a scream escaped her, a scream she thought would be terrified of what she had done to her brother, but instead the scream was triumphant, happy for achieving.
A part inside her was grieving for her dead cousin, but that part was small, easily over-shadowed by the maniacal, the mad part of her.
When she looked up, scanning the cavern for her fellow Death Eaters, she realized that most of them were tied together in the centre of the room by what seemed like an invisible rope. She looked up, and finally saw him, Dumbledore. She wasn't scared, strangely. She was ready to take him up as a challenge, ready to duel the only wizrd on this planet who had the potential to beat the Dark Lord. Oh, she was definitely not in control of her senses anymore.
A dark wizard came to duel her this time, and disarming him, she ran, ran away from Potter and his childish shrieks of "I WANT TO KILL HER!"
On and on she ran, teasing him mercilessly for taking her cousin's life, never feeling an iota of shame herself. And when the idiotic boy sent an Unforgivable toward her, she was done playing all games. "Potter I'm going to give you one more chance," she shouted. "Give me the prophecy—roll it out towards me—and I may spare your life!"
And when he spoke, he spoke words that scared her to the bone, though she'd never admit it. "Well you're going to have to kill me, because it's gone!"
And when she knew that it really was gone, she also knew that she was as good as dead, as her master had spent a year luring the boy to it for a reason. "No!"she screamed, hysterical. It isn't true, you're lying! MASTER I TRIED, I TRIED—DO NOT PUNISH ME—"
And when Voldemort appeared there she knew that she was doomed. He spoke in that calm, raspy voice that meant that there was surely going to be trouble ahead for her, and even though she tried to explain herself—how she was fighting her worthless cousin when the prophecy smashed—she was paid no attention to, for her master's eyes had found Dumbledore.
They duelled, an exchange of curses Bellatrix could not properly see, and suddenly Voldemort wasn't there anymore. "MASTER!"she shrieked, terrified that he had left her here alone, where they would surely put her in that horrible, horrible prison.
Voldemort reappeared, transformed into that snake for dramatic affect (that much she knew), and grabbed her and disappeared. So someone hadn't left her to rot—she wasn't entirely worthless.
Once they reached their hideout, Voldemort spoke, "Now as you must have seen, those Misistry people know that I am back, we need to be a hundred times more cautious, more prepared, quite unlike today, where you were outsmarted by kids, Bella. I will spare you this time, but understand clearly, if anything of this sort ever happens again—you know what I am capable of doing."
"I understand, Master," she replied, her voice trembling.
As the months passed, she made no mistakes, pleasing Voldemort, and herself. She wasn't even sure if she was herself anymore. Where had the thoughts he had once kept close, the morals she had valued disappeared?
Then came The Battle of Hogwarts, her doomsday.
When the last spell hit her, she didn't know whether it was bliss or regret, but she knew that at last, she was free.
Written for Hogwarts School of Witchcraft and Wizardry, Assignment 11, Notable Witches and Wizards, Task 10: write about an unstable character