To clarify, many if not at all of the themes of this setting/story framework are inspired by/influenced by and in some cases essentially ripped off from in no particular order
-Warhammer 40k
-Crossed by Garth Ennis (don't click away, be patient, I'm not a fan either)
-Halo
-Starship troopers
-Real life military technology
-And other sources I can't really think of off the top of my head at the moment.
But what really inspired this? Partly ideas I've had for stories about inhuman supersoldiers bred for war descending upon alien civilizations and laying waste to them, but mostly this piece of Warhammer 40k fanart
Badass right? I've thought about this image for months. Only thing I'd change is the tank being smaller, more realistic in proportions and armaments and it being on treads. Anyway this image laid the groundwork for an entire Sci-fi setting. Let's get into it
The Universe
The overarching setting is the milky way galaxy, in some permutations of the setting (I haven't exactly nailed it down yet, but the details described herein are by and large "hard" and exist across the various permutations I've mentally devised) it is ruled in it's entirety or in part by a Human Empire lead by a series of mortal Emperor's (and when circumstances demand, Empresses) who in an effort to free their populace by and large from the horrors of war (against themselves and other threats, in some variants of the setting The Empire fights rebels, in others to unite disparate humanity under one banner, one Empire, and in a few against hostile aliens ((I am largely against including Aliens)) ) The Emperor's of times past decreed the creation of advanced Super soldiers, completely identical to one another (the name of which I have 100% down but in the 1 in 1 Trillion chance I ever even attempt to publish this will keep it private) bred for war, humanoid but not human. They are physiologicslly and mentally different. Their skin milky white, eyes human like and light blue (an arbitrary aesthetic choice by The Emperor that decreed their creation long ago). Their organs are resistant against damage from disease, injury and radiation. Their Nervous systems hardened against blast over pressure. They can go days longer than any man without drinking, weeks without eating. They are completely hairless and have no names of their own, identified only by serial numbers tattooed on their foreheads. They are massive and freakishly strong, 8ft tall and capable of deadlifting 1000lbs with ease when out of armor. They lack genitals and are incapable of conventional reproduction, they emerge fully grown and intelligent from gestation vats (training occurs in vitro via a kind of prenatal brainwashing). Psychologically they are cold, calculating and logical. They do not hate, they do not fear, they obey their central directive, Defend Humanity. Their armor being great mechanized suits standing 10ft tall, equipped with the finest sensors (Night Vision, Thermal Imaging, Radar) and subsystems (HUD's, Active Protective Systems,) The Empire fields and painted and repainted in camoflague minutes if not hours before deployment to various worlds. Their weapons mighty and terrible autocannons capable of turning Any conventional vehicle that isn't a main battle tank to scrap metal in a few bursts and pulping infantry. There is but one problem with these super soldiers, they are out of production and have been form some time. Not because Humanity forgot how to make them. They were deemed by The Empire too costly and time consuming to grow, The Nobility did not want to continue paying to create such living weapons of complete overkill. They decided they would birth a new generation of super soldier, the Second Generation [Donut Steel Supersoldier name].
In all versions of the setting the 2nd gens are smaller, weaker, cheaper and quicker to grow versions of the 1st gens. They are similar in many ways to the 1st gen (milky white skin, eyes, lack of genitals etc) but are also ill disciplined, cruel and sadistic. They wield conventional firearms and wear advanced but conventional armor. A constant in every variant of the setting is that the 2nd gens carry a deadly flaw, if they go too long without engaging in battle they enter into a state of irreversible psychosis and start slaughtering, torturing and destroying everything they can get their hands on. Except their fellow 2nd gens. This is where I start getting into bulletpoints.
-In all versions of the setting, the main event is a galaxy wide civil war between Humanity, their loyalist 1st gen supersoldiers and the psychotic 2nd gens, who by orders of magnitude outnumber their enemies in terms of troops under arms.
-Another constant is an initial slow but inevitable grinding defeat for the good guys until the leader of the loyalist supersoldiers goes before The Emperor and says "Restart the creation of my kind and grant me supreme command of all Imperial Forces and and I will win the war" to which The Emperor reluctantly agrees, setting the stage for events to happen later.
-The leader of the supersoldiers, being the most cold and logical of all his brothers, will do what it takes to win (and fulfill his mission of Defending Humanity) without being burdened by emotions or conscience. He will restart production of his kind under emergency protocols, quickening their production but drastically reducing their lifespans, he will reintroduce military service to humans and raise great armies of them, out of those who prove exceptional he will funnel into enhancement and augmentation programs where not all will survive the process, but those that do will emerge barely human in their capabilities. He will reorganize and streamline anything and everything, ignoring the hysterical cries of Imperial officials. He will destroy entire planets (after making every possible effort to evacuate it) if it means winning the war, eventually.
-Story would largely focus on the loyalist supersoldiers themselves and the people (soldier and civilian alike) and officials they interact with interspersed with vivid descriptions of battles across the Galactic war front. Would probably also have World War Z style side stories exploring various different places and situations from the perspectives of anyone but the rebel 2nd gens).
-The story would in all variations have plot threads about political debate and conspiracies. The Emperor would grow increasingly paranoid about the growing adoration of his appointed supreme commander that, increasing geometrically after each of this victories, which come increasingly rapidly as the war nears its end.
-Pretty much near universally across all variations the story concludes with the defeat of the 2nd gens and shortly after a coup against The Emperor by the 1st gen leader as he does not trust humanity to not destroy themselves (His directive is too defend humanity, remember, even from themselves). After which he becomes a benevolent dictator to a largely approving Imperial populace.