Compared to some of the other dynamics in the Harry Potter, Sirius and Bellatrix's was rarely in direct spotlight, whether in the books or the movies. They have, however, one of the most interesting and intriguingly unappreciated relationships in the series.

First of all, their parallels -- they were both prisoners of Azkaban for over ten years, making them both sullen, depressed, haunted individuals who are overly familiar with battling for sanity and hope against the dementor's oppression. The difference? Sirius pulled through, Bella gave in. Still, even if Sirius was strong enough to avoid a complete mental breakdown, you can still see that crazed, rabid look in his eye sometimes. They both held onto hope to keep them going-- Sirius to the hope that he would escape and find Harry, and Bella to the hope that Voldemort would return and save her. They're both Blacks, pureblood elitists by birth, and quite honestly they both probably would have stayed that way if Sirius had been sorted into Slytherin. And they are a nearly even match in a duel.

I chose a couple of passages from the books I thought were particularly intriguing. Let's start with Harry and Sirius's discussion in Grimmauld Place:

"You never said she was your-"

"Does it matter if she's my cousin?" snapped Sirius. "As far as I'm concerned, they're not my family. She's certainly not my family. I haven't seen her since I was your age, unless you count a glimpse of her coming into Azkaban. D'you think I'm proud of having a relative like her?"

"Sorry," said Harry quickly, "I didn't mean- I was just surprised, that's all-"

"It doesn't matter, don't apologize " Sirius mumbled. He turned away from the tapestry, his hands deep in his pockets. "I don't like being back here," he said, staring across the drawing room. "I never thought I'd be stuck in this house again."

This is the first time we get a glimpse into their dynamic. Obviously, Sirius is still bitter and resentful towards his family, especially her. He hates almost everything about them-- their elitism, their cruelty, their loyalties-- and he certainly isn't ignorant of the cruel acts of torture his cousin has committed over the years.

I think that, despite the fact that he knows he morally opposes to everything the Black family stands for, so much so that he's embarrassed to be related to them, it still hurts that they disowned him. He may have convinced himself that the Potters were his real family after leaving Grimmauld Place, but that doesn't change the fact that he has memories of his blood family -- Regulus, Orion, Walburga, Bellatrix, Narcissa -- and some of them are bound to be good ones-- ones he certainly does not want to be reminded of as he tries to maintain his mental image of them all being monsters, all the time.

Next, here's my favorite scene in all the books:

Dumbledore sped down the steps past Neville and Harry, who had no more thoughts of leaving. Dumbledore was already at the foot of the steps when the Death Eaters nearest realized he was there and yelled to the others. One of the Death Eaters ran for it, scrabbling like a monkey up the stone steps opposite. Dumbledore's spell pulled him back as easily and effortlessly as though he had hooked him with an invisible line--

Only one pair was still battling, apparently unaware of the new arrival. Harry saw Sirius duck Bellatrix's jet of red light: he was laughing at her.

I cannot stress how much I love that imagery. You're given this picture of Dumbledore, debatably the most powerful wizard of that time, guns blazing, causing this huge scene and sending Death Eaters flying away in fear. Every pair of duelers has stopped, the Order is watching and the Death Eaters are retreating. Everything is in chaos. I would assume this drastic change in atmosphere is kinda hard to miss. And yet-- here Bellatrix and Sirius are, so completely absorbed in doing their own thing that they don't even notice.

I immediately thought of those cliche ballroom scenes where the pair is so enchanted and consumed by one another that they don't that the room is on fire. Or the ship is sinking. Or the zombies are attacking. You know, that kind of vibe. Only less of a romantic sense and more of a deeper connection, rivalry, compatibility. You know, like Batman and the Joker. The perfect rivals-- equal in almost every aspect, and twice as much fun.

Seriously though, they are so completely lost in their own little world of combat they don't even notice DUMBLEDORE. Both are talented duelists, and I would assume they are not completely unfamiliar with one another's tactics (I like to think they were quite close before Sirius was disowned and thus had play fights often). They clearly both enjoy the thrill of battle and the challenge of fighting each other (Blacks are notoriously excellent in duels, and it probably isn't often they find a partner who is an equal match for them). This is also likely the first time the cousins have seen each other since he was a teenager and Bella was mid-twenties (provided Sirius is to be believed).

They almost seem to be playing, as in, not actually fighting. We don't really get enough of a description of their duel to truly judge the nature of their duel, but we do know that neither of them were aiming for the kill shot. And why would they; having this much fun?

Moving on to the passage directly following Dumbledore's entrance:

"Come on, you can do better than that!" he yelled, his voice echoing around the cavernous room.

The second jet of light hit him squarely on the chest.

The laughter had not quite died from his face, but his eyes widened in shock.

It seemed to take Sirius an age to fall. His body curved in a graceful arc as he sank backward through the ragged veil hanging from the arch….

And Harry saw the look of mingled fear and surprise on his godfather’s wasted, once-handsome face as he fell through the ancient doorway and disappeared behind the veil, which fluttered for a moment as though in a high wind and then fell back into place.

I love the ambiguity in regards to the spell Bellatrix cast that sent him through the veil-- it leaves room for interpretation. Still, I stress: I honestly don't think Bellatrix meant to kill him.

That being said, I can't say I believe her opposition to killing him was very strong-- merely that she was caught up in the moment of the duel, enjoying the battle too much to want to end it quickly. Because, as we all know, Bella had no mercy for family members who betray the name. If she wasn't aware that Dumbledore had entered the battle, it's easy enough to believe she had forgotten about her surroundings as well, thus the veil behind Sirius.

Of course, I must acknowledge the triumphant scream she gives once he goes through-- yes, she won, and the person who had disgraced her family was dead-- I'm not at all trying to imply that she was deeply torn up about it (not instantaneously, at least). At the end of the day, she was justified by everything she believed in killing him: she killed both a valuable member of the Order and a blood-traitor to the Black family. Frankly, they're in the middle of a war in which they belong to opposite sides. Killing the other guy is kind of what you're supposed to do.

Lastly, I love the parallels between Sirius' and Bellatrix's death scenes:

"You - will - never - touch - our - children - again!" screamed Mrs. Weasley.

Bellatrix laughed, the same exhilarated laugh her cousin Sirius had given as he toppled backwards through the veil, and suddenly Harry knew what was going to happen before it did.

Molly's curse soared beneath Bellatrix's outstretched arm and hit her squarely in the chest, directly over her heart.

Bellatrix's gloating smile froze, her eyes seemed to bulge: for the tiniest space of time she knew what had happened, and then she toppled, and the watching crowd roared, and Voldemort screamed.

In her last moments, Bellatrix reminded Harry of Sirius. And really, looking at the two passages back to back, the resemblance is uncanny.

Their own arrogance is their downfall. Both Bellatrix and Sirius spur on their opponents with their taunts, leading to them being hit squarely on the chest. The both of them die with smiles still on their faces, yet with eyes widened in realization and fear.

This is why, although their dynamic was never explored in great detail, it was my favorite in the series.