Born on the colony of Waterloo to parents firmly entrenched in the world of business, Rossi bucked family tradition by showing little aptitude for commerce and less interest in following in his parents' footsteps. Instead young Serge enjoyed the strenuous life of athletics and organized sports, and it wasn't long before he started talking to the Alliance recruiters who visited his school. He payed lip service enough to them long enough to graduate high school, before promptly enlisting in the Alliance Marines.
A meteoric ascent up the junior enlisted ranks followed, and it wasn't long before the Alliance decided that Corporal Rossi might do fairly well with bars on his shoulder instead of chevrons. Orders were cut for him to attend officer candidate's school, and Rossi was yanked out of his infantry platoon and sent to Luna Base to learn the ways of the officer.
Unfortunately for Rossi, rather than being given a platoon to command, he was made executive officer of an infantry company. He served capably, if unhappily, in this posting, during the first stages of the human-batarian war. By the time of the Battle of Torfan, Rossi had acquired his First Lieutenant's bars and a reputation for bulldog tenacity when he was actually able to make it out onto the battlefield, and more than a little bitterness he'd yet to hold his own command.
The meatgrinder of Torfan proved to be his chance: when his company was butchered by a batarian nerve gas attack and the CO killed, Rossi took command of the battered remnants and pulled them back to base. Unable to afford rotating anyone off the line, the Alliance kept Rossi's men in the fight as a rear-echelon security element.
After Torfan, higher headquarters kept Ross in another staff posting. While this was considered an excellent developmental position for anyone looking to pursue a career, for Rossi it was a dull, boring dead-end. When his term of service was up, Rossi walked away from the Alliance and never looked back.
The Blue Suns
Unfortunately, Rossi hadn't completed any higher education, and while he was skilled at the trade of the infantry, that hardly translated well into a civilian career. With his savings dwindling fast, he took up work as a security guard on Bekenstein. Hardly the adrenaline rush of action, but it was a hell of a lot better than not getting paid.
One year passed, and Rossi discovered, quite by chance, that there was in fact an alternative. A convention for the private military industry was on-planet, and the ex-Alliance officer decided to have a look to see what all the fuss was about. The first booth he wandered up to, quite by chance, happened to be the Blue Suns' recruiting table, staffed by one Arthur Daye and his batarian subordinate Friegsid Khor'shok.
The two officers, realizing the grim fveteran obviously wasn't another wannabe kid, gave him the usual sales pitch. Rossi, feeling adrift on civvie street, bored, and more than a little keen to make some good money, signed on that day.
While some in the Suns like Major Daye received a promotion as part of their signing on with the corporation, Rossi wasn't quite so lucky. Given a Lieutenant's rank and pay, he was given charge of a platoon out of 93 Commando, under Captain Jonathan Nielson. A fellow frenchman, the generously mustachioed Nielson considered himself heir to a long tradition of mercenary soldiering by his fellow countrymen. Nielson had given his unit the nickname of Les Affreux -- the Frightful Ones, an appellation dating back to older earthbound mercenary units. Unlike "Katamayla" Khor'shok's disciplined and squared-away 92 Commando, 93 was a much more buccaneering outfit -- ferocious in battle and hard-drinking off the field.
With a culture like that, the stoic Rossi had trouble finding a place in the unit. While his habit of peppering his speech with snippets of their native language endeared him to Captain Nielson, his men were considerably less fond of him. Rossi insisted on his men conducting themselves with military discipline and learning basic drill. Accustomed to much more lax supervision, mumbling began to circulate amongst the platoon about fragging their new CO.
That changed with Rossi's first deployment. The Yndolan Civil War, a brutal struggle between the planet's central government and the well-armed breakaway faction that had been bedevelling them for a year, was 9 Commando's next deployment. After several actions, the mumblings had stopped, and a new sense of pride had taken hold in Rossi's platoon.
By the time of the stand-down on Omega, Rossi's platoon had become Captain Nielson's go-to unit. And when the Adjutants blitzed their barracks far from the safety of the Suns HQ at Katange Arcology, 93 was the first unit to stand-to and try repel the invading aliens. Despite the efforts of 9 Commando to stem the tide, the aliens overran their positions in fairly short order, inflicting heavy casualties and infecting numerous Suns. Captain Nielson was the last one to fall, infected by an Adjutant while covering the retreat of his sub-Commando onto their transports---and shot in the head by Rossi before he could fully turn. When the Ninth made it back to Katange, a weary Major Daye gave him command of 93 Commando.
The unit soon received a new contract in a new place -- new for Rossi at least. For the rest of 9 Commando on the other hand, the jungle world of Katamayla was a return home, of sorts, to the unit's birthplace. Rossi hadn't experienced the incompetence of the rebel forces on the original Katamayla contract, so the newfound tactical competence of the rebels didn't take him by surprise like it did his fellow sub-Commando leaders who'd expected an easy fight. 93 acquitted themselves well in their first actions under Rossi's command, but he could do nothing to prepare them for their true enemy.
The Reaper invasion of Katamayla absolutely butchered 9 Commando. Retreating from the capital to the bastion at Kuvabu, Reaper Destroyers descended on the fleeing vehicles like angry gods, annihilating 91 and 94 Commandos to the last man, and inflicting absurdly heavy casualties on 92 and 93. Rossi and his men fought like hellcats on the retreat, and during the breakout from Kuvabu. An impressed Daye and Dunn noted Rossi's tactical abilities -- and administrative skills at keeping his unit supplied and equipped and simply fighting overall during the siege at the bastion -- made the man XO of 9 Commando.
Luckily for Rossi, being XO under Major Daye was considerably different than being one of a UNAS unit. Not trusting any "staff puke" unwilling to get their hands dirty, Daye insisted on Rossi accompanying him to the front, a command which the Frenchman readily accepted. Assigned to Task Force Hammer's aggregation of Big Three units, 9 Commando was selected to lead the charge to liberate a Reaper processing camp on London's outskirts. Despite some friction with their opposite numbers in Eclipse, the column managed to make good headway before a blue flash interrupted matters.
Having taken heavy casualties in the War, 9 Commando's top goal afterwards was to rebuild the unit. While there was no shortage of blooded veterans looking to sign on with the Suns (courtesy of the increase in pay), there was a significant difference between the operating styles of the various governmental forces and the Suns' mercenaries. As XO of the Ninth, Rossi found himself handling the majority of the administrative work as the unit began to build itself back up to full strength, though he found time to abandon his datapads when Daye asked him to help Centurion Dunn in enforcing discipline amongst the recruits.
Fortunately, the Suns soon received a new contract, one on a world trying to gain independence from the Vonskar Coalition, a world with massive eezo deposits. Rossi, by now quite familiar with Daye's operational style, was at the Major's side during the heavy fighting on Tshombesha. Unfortunately the Captain's luck ran out during the battle for the capital Elizabeth, and Rossi fell to an Eclipse sniper, intercepting a round meant for his commander.