Always important to remember that all verses are subject to change and tweaking as needed for interactions. I personally do not think it's in the classic 'multi-verse' way but to make it easier, we can go with that as a default. Do not be shy to approach with questions and different ideas. I am always willing to try new things if it has been properly discussed beforehand.

COUNTRY PUPPY TURNED SOLDIER

Being a country boy for the rest of his life, was simply something that Zack could not conform to. In his heart, he wanted to be one those heroes so often read about in the newspapers because that’s what he felt was his true dream. It’s why he scurried away to the city of Midgar and successfully joined SOLDIER, where he caught the eye of Angeal Hewley, a renowned 1st Class. Taken under his wing, Zack restlessly trained and exceeded expectations when deployed on duty, eventually earning him the promotion to SOLDIER 2nd Class. But before that, he went through the same entry level torments that all other young men do, not only having to adapt to a life in the city but to day after day of both dull and rigorous tasks.

SOLDIER 2ND CLASS ZACK, ON THE JOB!

Acquiring the 2nd Class rank, Zack was one step closer to fulfilling his lifelong dream of proving himself and becoming a hero. Even when others doubted such a goal was even possible, he would not allow himself to falter in his resolve, training and taking his mentor’s lessons and words with the utmost admiration and respect. When Angeal recommended him for a promotion to 1st Class, he was more than ready to demonstrate how worthy he is when deployed to Wutai during the war. Thanks to the combined efforts of the Shinra forces, the war came to an end but it was a bittersweet victory for Zack, following the disappearance of his best friend and mentor in the process. 

SOLDIER DOESN'T MEAN MONSTER

The promotion to the esteemed 1st Class SOLDIER rank, left a bittersweet taste in the young man when being introduced to the darkness of the company’s who’s elite forces he belongs to. In the wake of the incidents and conflict, Zack finds his beliefs questioned and put to the test. But even when faced with the death of one of the most important people in his life, he remains steadfast in his dream and becomes an inspiration to others below him—Especially under the cloud of uncertainty that fell upon SOLDIER when losing so many of the members. The greatest blow was when the one hailed as the best of them, the war-hero Sephiroth, succumbed to madness and burned down an entire town before being reported dead by the company. Along with him were Zack and Cloud, who were taken as test subjects for Project S. 

EMBRACE YOUR DREAMS, PROTECT YOUR HONOR

Now on the run from the company they once worked for, Zack fights hordes of Shinra troops for the better part of a year, after escaping from where they were confined as test subjects in Shinra Manor, back at Nibelheim. Unlike his best friend, who was left in a catatonic state due to the intense mako exposure, the runaway former SOLDIER was seemingly spared of the adverse effects of the Jenova cells injected into them; due to the pre-existing mutation of his already enhanced body. The experiments did augment those enhancements and endowed him with greater strength and power in his abilities than what he previously possessed. All of it, however, proved not enough when ultimately faced with an ambush of the Shinra army just before reaching Midgar. 

THAT EX-SOLDIER MERC: SURVIVAL 

Alternate Crisis Core ending. Emerging victorious from the confrontation with the army, the former SOLDIER drags a still mako dazed Cloud and together, they resume what remains of their way back into Midgar. After nearly five years of disappearance, they finally reach the city and manage to hide with the help of the Turks. As decided while on the road in the back of a truck, he started to make a name for himself as a mercenary to earn money, realizing that his dream still endured but that now he would have to become the hero of those who employ him first. The rest, he was certain, would follow and fall right into place. 

A REUNION: ADVENT CHILDREN

The day Zack and Cloud were ambushed by the Shinra army, the former SOLDIER collapsed and bid his best friend goodbye with his dying breath. However, shortly after the younger man left, the seemingly maimed body was recovered and returned to Hojo’s custody. Against all odds, Zack’s heart was still ( faintly ) beating. Using the restorative and preserving qualities of mako as part, the man survived though he would once more be taken as a test subject; confined to a secret underground laboratory that only Hojo and those directly working for him, were aware of its existence. With the goal of Sephiroth’s Reunion in mind, the mad scientist maintained the once SOLDIER captive but with the fall of Shinra and the events that led up to and followed Meteorfall, the self sustainable location was abandoned. It would be two years after the disastrous day, that someone would discover the underground laboratory and find Zack suspended inside the tube of mako. When he recovers full consciousness, he will learn that the world was a very different place. 

DESTINY'S CROSSROADS: REBIRTH

Did something go wrong or did something go right? After surviving the ambush in a seemingly miraculous turn, Zack knew something was amiss following the strange burst of light that exploded from the city. When he returns, he finds half of the city destroyed and an unconscious Aerith that he rescued from the clutches of Shinra. Elmyra Gainsborough welcomes both him and Cloud to her home, but the sight of a rift in the sky has caused for everyone to resign to their fate, claiming the world is ending. Zack tries to figure out what's happening and what it could all possibly mean, all the while taking care of Aerith and Cloud; which leads him to venture out in search of a way to wake his best friend. That is, before learning Biggs plans to undergo a suicidal mission by blowing another reactor. Filled with indecision, his choice would ultimately lead him to his own fated death—Until the an encounter with Sephiroth sends him down a swirl of Whispers. Wandering in an endless space of white, he ends up crossing into Cloud's world, where they briefly face off against Sephiroth. Torn apart again, their fight continues individually, though still somehow connected, until the battle is won and Zack is pulled back to the world he came from. Waking in Aerith's Church to a blooming bed of flowers, the ex-SOLDIER is determined to find a way for their worlds to merge again. 

A REAL LIFE HERO [ MODERN AU ]

From a young age, small-town boy Zack Fair knew what he wanted: to get away and live a great life filled with excitement and recognition. The obvious choice ( for one who has been groomed under the government’s regime of superiority ) was the military forces, to proudly serve under the ‘greatest country in the world’. It’s not until he actually joins the ranks of the military, that he discovered something better, that fills him with satisfaction and accomplishment: the Combat Search and Rescue unit. Sometimes it was simple and posing no risk but others, his duty took him to dangerous warzones or hazardous disaster areas that often put his very life on the line—Even though he would knowingly and willingly do so if it means to save others.

ELITE S.O.F. MONSTERS [ FF7 MODERN AU ]

Only a skilled and talented few of the military forces are selected for the most elite Shinra private SOLDIER units. With a plutocracy being established decades ago under the robustly wealthy Shinra Company, the independent country of Midgar has become one of the most powerful in the planet of Gaia. They have managed to remain in power by monopolizing mako energy, a source that comes from the very earth itself: the same that also makes soils fertile with life-giving qualities. Lesser opposition found in the form both of countries and ecologist organizations have tried to overthrow them, but always fail thanks to Shinra’s SOLDIER units: a force composed of physically enhanced humans. Zack is one those men and women often sent to special assignments above from the rest of the military, be it intelligence gathering, infiltration, or direct combat situations at the front lines. With all information and communication censored by the Company, it was difficult to become aware of what transpires behind closed doors; but the more Zack accomplishes, the more he was exposed to the truth. Their country’s false benevolence threatened to not only destroy others, but to doom the planet itself.