In the tradition of the excellent author known as Case13, here is a series of short vignettes. I think that, if you know the above author, you'll recognize this format.
Pre-Serenity, post-Firefly.
Malcom Reynolds, once a Sergeant in the bloodiest, most decisive battle of the Unification War, now just a Captain. His coat is brown. "Brown-ish," he might say casually, and wave the subject aside. But his brown coat weighs far more heavily on his soul than on his frame, and in his heart, he's still fighting.
Mal lost a thousand men and women in Serenity Valley, but he made the Alliance pay nearly triple in the cost of bodies. He still dreams of breaking the Alliance, but even he knows, deep in his heart, that no matter what the name of the government, there will always be some degree of rot somewhere in the center.
That is why he no longer fights for Independence. He doesn't have to; his Independence is in the black between worlds, where he answers to no one, least of all a corrupt government. No, Mal fights for one reason only:
Mal fights for River, and her independence. Mal loves River Tam, as Gabriel Tam should have loved his daughter. Mal fights for his Albatross, his symbol of fortune and freedom, he fights to protect her, and because he can do all the things that Simon can't. Mal can kill men without blinking, and when it comes to the safety of the abused girl, Mal would cross any line. If he were completely honest with himself, Mal would even let Zoë die if it meant that River would live.
He hopes it never comes to that.
Zoë Washburne fights because she cannot stop fighting. She can't let go of the fact that the Independent Command betrayed their own troops and left them to die at the Battle of Serenity. Zoë's curse is being unable to forget the faces, voices and names of every Browncoat who walked into that valley and never left.
An eidetic memory is excruciatingly cruel that way. Zoë literally cannot forget, and though she doesn't show it, it haunts her. She hates the Alliance more than anything else, and nothing can ever change that. The Alliance took her family, her friends, and her troops, but then they took something that she can never forgive them for:
They took away her revenge.
The Allied commander who'd ordered the attack on Belial, the Rim world where she was born and where her family was slaughtered, the man whose miserable existence was Zoë's reason for entering the war, was executed not three weeks after the Allies announced victory.
He wasn't even executed for ordering the attack, but for raping another official's daughter. So the sins he committed against Zoë go unpunished.
The most she can do is transfer that hate to whomever she has to kill, but it doesn't keep.
It'll never keep, though, and so she'll never stop.
Hoban 'Wash' Washburne fights because he has to. He's not a coward; he just doesn't care much for violence, is all. But he loves to pilot Serenity, and he loves Zoë, and because he can't have them without fighting, he'll accept the bad with the good.
Privately, Wash is in favor of the planets being under an alliance. Not the Alliance, but an alliance. Wash has seen far too many evils not only perpetrated by the Alliance, but sanctioned by it, to fall into the fantasy that the Allied Government is for the benefit of mankind. But he's also seen too many planets that are just this side of survival, lacking basic necessities, to allow the dogma of 'independence' to take root. Wash believes that there needs to be peace and understanding between the Core and the Rim, and that the essentials should be shared and freely so.
But the Captain and Zoë fight, and they can't fight without him, so he fights too.
He doesn't ever talk about his beliefs, and nobody asks. Because, hey, he gets to pilot a ship and play with dinosaurs! And he has a very sexy wife, if he says so himself.
Which he does. Often.
Inara Serra doesn't fight. Not physically, although she can. It would surprise everyone aboard the Serenity, save for the reader River, to know that Inara is one of the best swordswomen in the entire 'verse. Her crossbow is a toy to her, though - her sword is her only 'real' weapon.
Inara fights with words and wit and charisma, because, as skilled as she may be with a blade, her tongue is infinitely sharper. Unlike Mal and Zoë, she doesn't fight for people, and unlike Wash, she doesn't fight because she has no choice.
Inara fights because she's addicted to the thrill. When the battlefield is a table, and the weapons of choice are words, she loses herself. Inara's entire soul sings in exultation during a debate. She loves the intricacies and subtleties of wordplay - to her, there is no higher art form than that of a well-laid argument.
And if Mal could keep up with her verbally and not result to cheap insults, she would readily admit that she loves him, too.
Shepherd Derrial Book doesn't fight anymore, although he used to. He has long since given up on the path of a warrior and devoted himself to God.
His fight is with Mal, and it's a fight of faith. Book was once an Operator, the top echelon of the Alliance's Operatives, until he sickened of the bloodshed he caused. Book stepped down and entered the Abbey and found forgiveness from God.
Book loved to fight, and because of its inevitable conclusion, he gave it up forever. He misses it, though, because as much as he hates to admit it, fighting is where Book's talents and desires lie. Always exhilarating, always exciting...and when all is said and done, Shepherd Book loathes boredom. Boredom (or rather, the lack thereof) is part of why he's stayed on Serenity for so long.
But mostly it's because of Mal. He knows it's never too late to change, and that is why he fights so hard for Mal - because Book genuinely likes Mal, and he genuinely believes that Heaven would be a very dull place without Mal in it.
Kaylee can't fight. She can't stomach it. Violence, on anyone's part, for any reason, makes her physically ill. Kaywinnet Lee Frye isn't really a pacifist, though; she simply believes that everyone has a right and a reason to be appreciated and loved.
Love is a very key word with Kaylee. She does love her Captain. And she is in love with Simon. And because Mal loves Inara (though he won't admit it) and Zoë (though he wouldn't call it that), Kaylee loves them too. Kaylee loves Wash because Zoë does, and she loves River because Simon does. Kaylee even loves Jayne and Shepherd Book, if nothing else than the fact that she doesn't know who does love them. But it is love, and it is very real.
And she loves Serenity. And because she knows her duty is to her Captain, whom she loves, she fights by making sure Serenity can. Serenity is her home, and its crew are her family, and if there's anything that a Frye looks out for, it's family.
Kaylee loves her family. And that is how she fights.
Simon won't fight. It is beneath him. Leave the puerile displays of aggression to the lesser Homo Sapiens - any man can destroy; but few can heal. Simon cares nothing for the laws of the Alliance, and frankly he cares even less for Mal and his orders. Simon's highest aspiration is not even to protect his sister, though he doesn't realize it. And he would deny it to death, honestly disbelieving, if it was pointed out.
No, the only Law Simon believes in was set down by Hippocrates thousands of years before. "First, do no harm..." is always at the forefront of his mind. Though he dearly loves his sister, the violation of that Oath by the doctors at the so-called 'Academy' on Osiris horrified him more. Not by much; just a hair. But still more. It was because of River that he went, that is true, but it is because of his rage at the doctors' callous disregard for this greatest commandment that Simon succeeded.
Had he not known the specifics of what they were doing to his sister, Simon would have never brought the stun-grenade hidden in his cane. 'Apt punishment' is what he considers his actions to be, and sees no discordance between them and his Oath. He would never have even gotten close to the academy, because he would have tried to go through 'proper' channels to protest River's treatment.
And Simon would have had an 'accident'. So while he does not know it, his adherence to the Hippocratic Oath is why Simon is alive.
Simon stays with Mal because Mal protects his sister better than he can.
And in a way, he hates Mal because of it.
Jayne Cobb's reason for fighting, if you were ever able to drag it out of him, would startle all those who claim to know him best.
He doesn't fight for money, although it's nice. He doesn't fight for recognition, because he doesn't care. He doesn't even fight because he thinks it's the right thing to do. Jayne Cobb fights because he loves.
Jayne loves exactly three people in the entire 'verse, and it's on account of them that he does what he does. Jayne Cobb loves his mother, and because she can't provide for her family and herself near as well as Jayne feels that she deserves, Jayne fights and sends the vast majority of his paycheck back home. Jayne is cognizant of the fact that, if it weren't for him, his mother would have to go to work, probably in the mines...and there ain't no gorram way that Ma Cobb is gettin' anywhere near one o' them feng le mines. So Jayne provides. And he's good at it.
Jayne loves River, too. Crazy she may be, just this side of surpassingly dangerous, but Jayne knows that it's not her fault that she's the way she is. Jayne, more than anyone else on the crew, hates Blue Sun for what they've done to River Tam, and if he hates them, he must love her. She scares him, true...but no child deserves what happened to her. In his mind, Jayne sees River Tam as his little sister. So now she has one who can heal her, and another who can protect her. And Jayne is very good at protecting.
And Jayne loves Kaylee. It's not romantic love - partially because Kaylee's eyes are only on Simon and partially because he doesn't believe he's capable of feeling that way around a woman - but it's love nonetheless. In his mind, Kaylee is something special and rare, and because of that, she needs to be protected. Jayne would, can, and has put his body between Kaylee and death before, and he would do so again. Easily.
And that's also partly why Jayne can never, ever stop hating Simon. Jayne still remembers how Simon essentially blackmailed Mal into protecting him and River, using Kaylee's life as a bargaining chip. Kaylee forgave him. Mal and Zoë reluctantly forgave him. Wash, Book, and Inara managed to forgive him.
Jayne can't. It takes all his willpower not to snap the Core-born hun dan's scrawny little neck. It's only because of Kaylee that he holds back. But the instant that the Doc screws up so bad that Kaylee won't have him back...crack.
And above all else, Jayne is extremely good at that.
River fights because she needs to know. She needs to know why this was done to her, why so much time and money was invested in her. Why the Alliance chose to make her a weapon, let alone the weapon.
She needs to know that Captain Daddy, Mrs. Zoë, Pretty Lady Inara, Sister Kaylee, Childish Wash, Devil-Haired Book, ge ge Simon and ge ge Jayne aren't risking their lives because she accidentally mentally stole the blueprints for some new Alliance Terraforming device from some visiting official. She fights to learn the truth.
That she's using the skills that the Alliance forced upon her to destroy them gives her a dark sense of satisfaction, but that is usually torn away with the inevitable wave of 'inner voices'.
She's a reader who's been stripped of her limbic system. She can't help but to know. Knowledge is power. And River is knowledge.
