Welcome to Operation: NORMALCY, a fanfiction universe created by H Eliaden Lowe (aka Hikaru Eliaden, Hikaru Yuy) for Gundam Wing focused on Heero Yuy and what made Heero...well...Heero. It explores his backstory leading up to the Conflicts of 195, and everything from 197 onwards with each "arc" of his life broken up into different series. Currently there is one prequel, three "operations" (aka arcs), and one sequel series.

Op. 00 - do not remember, do not regret
After Colony 170s to 180
Follows Aoi Kanagawa, an aspiring future political science major who meets a young man by the name of Odin Lowe in the courtyard of the collegiate institution they both just so happen to be attending (for wildly different reasons). It tells their respective backstories and how they eventually end up intertwining.

Op. 01 - Betrayal of the Highest Order
After Colony 181 to 188
Shiori Clark (nee Lipinskyy) managed to pull off what she considers the Heist of the Century. Her husband Seis is completely ignorant of the fact that the son he and his wife are raising isn't even his. Or hers, for that matter. Shiori heartlessly betrayed her best friend Aoi out of jealous and is now raising her son, now renamed Aiden, as her own full blooded offspring. Things come to a head when Seis finds out little Aiden isn't actually his, and it descends into a life full of abuse for the little boy who knows nothing of the truth. In the pursuit of the life Shiori's always wanted, she ends up tricked, and Aiden ends up back in the hands of his rightful parents...only to be ripped away from them again for a much different reason. With Odin murdered in cold blood by a member of their resistence group. Aiden wanders around X18999 trying to rejoin what's left of his family, and finds an old man in an alley who looks very out of place. "You've got good eyes, kid. How would you like to change the world and pilot a Gundam?"
Aiden's been striving to change the world for the better as far as the Habitats are concerned for the past two years of his life. If piloting this incredibly advanced piece of machinery is the way forward, he's willing to do whatever it takes to master it.

Op. 02 - Creating the Perfect Soldier
After Colony 189 to 195
Aiden, whose name is now "Beta", undergoes the training necessary to become not just a soldier and black ops agent, but to become the perfect mobile suit pilot. "Perfection" to the Barton Foundation involves experiments involving drugs and psychological abuse, among other horrors that anyone without the mental fortitude would've crumbled into nothing in the face of. Beta shows promise—he's familiar with the operation of mobile suits like the Leo, and he's a natural at it. He knows how to shoot and shoot to kill no less thanks to his father's training. All of these skills need to be honed to the deadliest of deadly precision. There is a price that needs to be paid for perfection, and Beta ends up paying that hefty price by sacrificing his sense of compassion and his emotions in order to become the "perfect soldier" and Dekim Barton's human death machine in the cockpit of a machine built for mass casualties. Until something goes wrong, and Beta isn't sure he wants to go forward with any of this when he accidentally steals the life of an innocent little girl...and is told he shouldn't care at all. Doctor J gives him a choice: either continue with Operation Meteor as Dekim wants, go to Earth and defect from the mission entirely, or go along with a modified and much more humane version of Operation M. Beta chooses Option 3 and J gives him a new name: Heero Yuy.

Op. 03 - Operation: Normalcy
After Colony 196-198
The war and conflicts and insurrections are all over. The dust is starting to settle. Heero, no longer a soldier of war or a weapon of death, has to find his place in a world where someone like him is redundant. What exactly is a life of normalcy? What does it look like? Heero's never known what a life full of life's mundane pleasures looks or feels like, but he's determined to live something just like that. Get a job. Finish high school. Get a degree. Get married and start a family. That last one, having a family to call his own, is the one that makes him the most nervous. Finding someone to put up with his bullshit and his trauma will be hard enough, but needing to juggle spousal responsibilities with parental ones on top of a demanding job as a Preventer field agent is a challenge that Heero both craves, needs, and wants to run away from. Lucky for Heero, Duo and Relena are both up for the task of helping the once perfect soldier transform into the perfect husband, perfect partner, and perfect parent. Heero doesn't have much time to learn about that last one, since his wife is due to give birth any minute now...
Read it on AO3

Op. 04 - Operation: Parenting
After Colony 199-252
Heero has to navigate life as a parent and all the trials, tribulations, and triumphs that entails. Heero doesn't have a very good road map when it comes to parental role models or figures. He ends up stumbling when it comes to correct parenting sometimes, but what parent doesn't? Heero knows what not to do with kids, which he considers better than not knowing anything at all. Duo and Relena help him succeed as best as they can, and parenting classes, therapy, and workbooks help him with the rest. Heero wants to lead a life that he can feel proud of—and that his kids can be proud of too. He doesn't want them to know how bloodsoaked his past is for fear the droplets will end up falling on them. Being a Gundam pilot is integral to who Heero is as a person, and the topic will at some point become unavoidable. Despite everything Heero's worked hard for, the waltz whose sheet music he thought he'd ripped up and burned in a fire has been rewritten, and those three beats are restarting themselves in a different starting formation than before. Or maybe it's more familiar than he realises. It starts with a call for reform and revolution, progresses to an assassination, and ends with calls for war. Unlike before, when Heero readily answered that call to revolutionise the world, Heero opts for silence in a world he deems unworthy. Permanent silence.
Read it on AO3

Op. 05 - Heavy is the Burden
After Colony 252 onward...
Heero's eldest son Aiden has to learn how to navigate life without his father's presence. It proves itself to be the hardest thing he's ever had to do. Aiden is his father's son and like Heero, Aiden's not great with dealing with things like "emotions" and "feelings" and "depression". He's constantly feeling like he's drowning in a tidal pool that constantly pulls and tugs at him trying to claim him for the ocean deep.
Read it on AO3