The Unification War was one of the defining incidents of the history of the Firefly universe. Despite this, and the effect the war's aftermath had on humanity at large, just what each member of the crew of the Serenity had done during the war was left a mystery during the show's original run.
Firefly was cancelled after one season consisting of 14 episodes but is widely considered to be one of the greatest "what-might-have-been" stories in television history. Critically acclaimed but doomed by a Friday-night time slot and its episodes being aired out of order, the show developed a cult following after being released on DVD. This led to a follow-up film, Serenity, in 2005, and the development of one of the most fanatical followings in all of fandom.
There has been talk of a Firely revival for several years, though little progress was made for a variety of reasons. Despite this, the original story of Firefly has continued in a series of graphic novels published by Dark Horse Comics and Boom! Studios. These books explored both the past and the future of Serenity's crew, with some of the stories further defining the Unification War and the surprisingly large roles that some of the series' main characters played during it.
Malcolm "Mal" Reynolds
Ironically, while much of Mal Reynolds' (Nathan Fillion) upbringing is a mystery, most of what is known about his life comes from his actions during the Unification War. Mal was a volunteer recruit into the Independent Planets army (i.e. the Browncoats) and rose to the rank of sergeant. Despite being a non-commissioned officer, Mal took command of a platoon during a long winter campaign on the planet of New Kasmir. This was likely due to all of the commissioned officers having died in combat, as Mal was unlucky enough to become involved in some of the war's bloodiest conflicts (including the Battle of Du-Khang, the Battle of Sturges, and the Battle of Serenity Valley) but lucky enough to have survived them. He spent the final days of the war following the Battle of Serenity Valley in a prisoner-of-war camp until he was released by the Alliance Army.
Zoë Alleyne Washburne
Zoë Washburne (Gina Torres) is another one of the few crew members of the Serenity whose life during the Unification War was definitively explained. Unlike Mal Reynolds, Zoë was a career soldier who fought with the Independent Army from the very beginning. She rose to the rank of corporal and served in the 57th Overlanders Brigade, serving in the same platoon as Reynolds for the final two and a half years of the war. They would go on to be the only survivors of their platoon following the Battle of Serenity Valley and spent the final days of the war in a prisoner-of-war camp.
Hoban "Wash" Washburne
Actor Alan Tudyk speculated that the Serenity's sarcastic pilot served during the Unification War, but that Wash's military career was not long or distinguished. Tudyk's theory was that Wash was shot down after a single mission and spent the rest of the war in a prisoner-of-war camp, entertaining the other prisoners with shadow puppet shows. While this theory is amusing, it has never been confirmed officially that Wash served in the military, though it seems unlikely the unorthodox pilot would have lasted long in such a constricted environment. According to the Firefly graphic novel Watch How I Soar, Wash avoided being drafted into either side of the Unification War, but he did consider enlisting since it could have been his ticket to flight school. According to the Serenity film novelization, Wash eventually paid his way to flight school independently and graduated second in his class. (Wash would have been first, but his classmate, the master hacker later known as Mr. Universe, made himself the top student.)
Inara Serra
It was Inara Serra's (Morena Baccarin) actions during the Unification War that eventually led to her renting a shuttle on Serenity. The graphic novel Serenity: No Power in the 'Verse revealed that Inara had a client who was a secret informant for the Independents. This client let it slip during one of their sessions that the Browncoats were planning a major offensive from a secret outpost on the moon called Fiddler's Green. Hoping to prevent bloodshed, Inara informed the Alliance of the attack and the location of the Independent base, not knowing that the Browncoats also used the site as a refugee camp. Somehow, the high priestess of the Companion Temple in which Inara served discovered what she had done. While Inara was not expelled from the Companion's Guild for violating their oath of confidentiality, she was exiled from her home temple with orders never to return, which led to her traveling the Rim worlds and eventually meeting Malcolm Reynolds.
Jayne Cobb
Not much is known about the man they call Jayne (Adam Baldwin) or his past beyond his being largely amoral yet good to his mother, though one Firefly episode was famously devoted to explaining how he'd become an accidental folk hero. A native of the planet Sycorax, Jayne was confirmed to have not served either side of the conflict during the Unification War. Just what he got up to during the war is anyone's guess, but it seems likely that Jayne was doing what Jayne does best – stealing and killing for the highest bidder and collecting more guns for his personal armory.
Kaywinnet Lee "Kaylee" Frye
The heart of Serenity's crew, Kaylee Frye (Jewel Staite) is another character who didn't get much backstory during the original run of Firefly. She took to starships at a young age in the same way baby ducklings take to swimming and learned the mechanic's trade at her father's knee. While the Unification War was being waged, Kaylee was on the planet Kowlonshi, helping her father with his work. She remained there until a chance encounter with a mechanic named Bester, whose incompetence and willingness to dally with local girls while on the clock set up the circumstances that led to Kaylee taking his job as Serenity's mechanic.
Simon Tam
Born into a wealthy family on the core world of Osiris, Simon Tam grew up ignorant of the realities of the Unification War, though he would later come to recognize the dangers posed by the Alliance government. As a youth, Simon supported the Alliance side of the war effort, though he never considered enlisting. At the time the war ended, Simon was still attending university, preparing to take the entrance exams to enter the Medical Academy at the University of Osiris.
River Tam
Like her older brother Simon, River Tam lived a privileged existence on the core world of Osiris. A prodigy who had been correcting the spelling of her older brother since she was three, River was still in school during the Unification War. River was said to be an enthusiastic student with a love of dance and sufficiently advanced that she entered into a graduate-level program for physics before she was 14.
Shepherd Derrial Book
A man of God with an uncanny knowledge of the shady side of the 'Verse, the life of Shepherd Book was one of the major mysteries of Firefly. Some of his history was finally revealed in the 2007 graphic novel Serenity: The Shepherd's Tale. Before he found religion, Book had been a thief and thug, who had been recruited to the Independents as a special agent. He later volunteered for a mission to infiltrate the Alliance under an alias and worked his way through the ranks to become a high-ranking commissioned officer, secretly sabotaging the Alliance's war effort from within. His actions led to the greatest military disaster in the history of the Alliance, with seven different strike teams meant to raid six key Independent installations and a space convoy being ambushed by Browncoat forces. Book survived only by sheer luck, having been quietly discharged without trial and shoved into an escape pod, after an ambitious underling had him declared unfit for duty. He apparently maintained his rank, however, as he had an IdentCard which secured his medical treatment from an Alliance cruiser in the episode "Safe."