The First

He steps back into reality and finds himself standing before the massive throne on which sits the regal rotting corpse of the being known through the rotting burning Galaxy as the Emperor of Mankind. Seated on his Golden Throne, he has been worshiped as a god by the innumerable masses of humans, transhumans, cyborgs, mutants, and monsters that make up his Imperium of Man. An empire just as rotten and useless as the dead man who rules it. In reality, it is ruled by psychopaths, sociopaths, zealots, and despots who use the excuse of doing the Emperor’s will as a motive to murder anyone who dares attempt to tell them exactly how insane they truly are. So, basically, they are the perfect inheritors to the dying cesspit of immortality, corruption, and idiotic stagnation as anyone.
“You have truly made a complete and utter shitshow this,” says the man in a tone of utter disgust, “Haven't you, son?”
The Custodians nearest to him hear him speak and realizing he is there for the first time attack. The man is the size of a normal mortal, only 6’1, with deep brown skin, a muscular build, and long snow-white hair. His eyes are pure gold without whites, which is the only thing that outwardly marks him as not human. He wears a simple shirt, a pair of blue jeans, and black sneakers, an outfit not seen on Terra since the world was called Earth. He has no weapons, and his hands are tucked lazily in his pockets. The two Custodian Guards, fully armored in their golden aurumite armor and armed with their Guardian Spears, dwarf him in every way. They move with a speed that no baseline human and few transhumans can match, covering the distance between them in less than three seconds. To the man standing before them, I might as well have been three decades.
With a flicker of a thought, he slows time around himself to a crawl. Both custodians freeze in place after only a step. He does this not because he needs to. These golden meat bags could hit him with every weapon and every ounce of strength they possessed for a thousand years and never move or scratch him. No, he does these because he still has words for the Emperor.
“I made you and left you to be the lead steward of mankind,” says the man, never taking his eye off his rotting child, “Instead, you decided that it would be better to rule and lead them down the path to ignorance. Basically, becoming little better than those Warp-born parasites you claimed to be protecting them from. I thought about dragging your ass back into this corpse and letting you truly suffer, but no, you can pull yourself out of that particular hell. Why I even bothered creating you, your cousins, or the human race is beyond me. I guess I was bored that week.”
He takes his eyes off his son and glances at the two Custodians still frozen in time. He considers wiping them from existence but tells himself they are only doing their jobs. Jobs they were created to do by his disappointment of a child. He decides to have mercy. There will be plenty of killing to be done before he gets this miserable Galaxy back on track. With another thought, he returns time to normal and completely deactivates their power armor. The two Custodians fall to the floor like rocks and slide to a stop at his feet.
“Just about as useful as him,” says the man.
Ignoring both, he turns away, stepping out of reality once again. When he reappears this time, it is in the middle of a full meeting of the Senatorum Imperialis, literally in the dead center of the Great Chamber of the Senatorum Imperialis. The raised voices were a moment before in the middle of an intense and no doubt important argument, likely about some world that was short on its tithes and had to be burned. The man could know each and every person staring at him wild-eyed if he were willing to put forward the smallest effort to scan their minds and souls. It would take about a second to do them all. That is, if he cared. He doesn't.
“The Imperium, as you all know it, is dead,” says the man in a voice that doesn't rise above speaking level but can be heard clearly through the massive chamber, “If you want to know who I am, my name is Genesis. I will be the one in control now. Your services, as half-assed as they are, will no longer be needed.”
An eruption of laughter follows more silence. Genesis, not in the mood for it, raises his hand and snaps his fingers. Everyone in the chamber disappears. He teleported them to random locations around the planet. Exactly where he neither knows nor cares. With the chamber now clear, he begins his work, pulling the entire human species from the mass extinction they seem determined to dive headfirst into.