I have taken your advice and extended this to a two-shot. Enjoy, you. Also, for the first part, either use your knowledge or lookup the warpchat, and the Emprah's name is Golden Boy.
Golden Boy: Oh, warpspawn! Guess what day it is~?
ICANHASGALAXY: DAY I CAN HAS GALAXY? YAAAAAA-
User: ICANHASGALAXY has disconnected due to unstable connection.
Citizen Khaine: I don't know, leg day? Khorne, what do you think?
RIPANDTEAR: It certainly isn't leg day BECAUSE THAT WAS YESTERDAY!
Grandpapa Nurgz: It's not our anniversary, is it, dear?
IshaMe: No, why don't we ask the resident 'know-it-all'? Tzeentch?
MasterOfPlans: Well, that's a rather loaded question. Is it the day a Tau ship spontaneously combusts? Is it the day that an Imperial Guardsman dies in combat? No, that's every day. Is it the day that Bethesda realizes that monetized mods are killing their reputation? Is it the day that-
Golden Boy: No, specifically a human holiday.
MasterOfPlans: Oh, in that case it's-
MasterOfPlans: …Father's Day.
Gorkz is Bestest: Ha, youz betta' get tah runnin', yah gitz! An' 'ow do yah uz dis bleedin' ting?!
Morkz is Strongest: Youz'e usin' it already, grot!
MaliceInWonderland: It's this day I'm glad I don't exist.
User: MaliceInWonderland has disconnected by user.
420BlazeMy3601337Vagick: TOO MUCH MUSCLE!
User: 420BlazeMy3601337Vacick has disconnected by user.
MasterOfPlans: HOW DID I FORGET?!
User: MasterOfPlans has disconnected by user.
RIPANDTEAR: TOO MUCH ANGER!
User: RIPANDTEAR has disconnected by user.
[Bazinga]: Khaine, we better leave, we don't want to get involved in this.
Citizen Khaine: For once, I agree with you, clown.
Users: [Bazinga] and Citizen Khaine have disconnected by user.
Grandpapa Nurgz: We should go, Isha.
IshaMe: Yes, lets.
Users Grandpapa Nurgz and IshaMe have disconnected by user.
Gorkz is Bestest: Howz do I leav' dis ting?
User: Gorkz is Bestest has disconnected by user.
Morkz is Strongest: Youz'e don' it already!
User: Morkz is Strongest has disconnected by user.
Golden Boy: Ah, the wonders of fear.
User: Golden Boy has disconnected by user.
The Imperial Palace:
In the throne room of the Imperial Palace, the Emperor of Mankind's psyche returns to his body on the golden porta-potty. He sees his son, Rogal Dorn, standing there building a fort around him. "Rogal, My Son. Get Your Head Out Of Building Because Some Stuff Is Going Down Right Now." Rogal turns to him.
"What is it, father? Have the orks invaded another forgeworld? The Ultramarines seemed to handle that just fine. They went and shot them a few thousand times and they stopped moving. Or has the Dornian Heresy finally succeeded in having tacos served on Fridays instead of Tuesdays?" That Heresy shall not succeed. Taco Tuesday sound much better than Taco Friday.
"No, But Rest Assured That Taco Tuesday Shall Prevail. Do You Remember That One Dude I Showed Off To All Of You Back A Few Thousand Years Ago? The One With That Big Gun And The Other Big Gun And The Slightly Smaller Gun And The Other Slightly Smaller Gun And- You Get The Point?" Thinking back a few thousand years, Rogal remembered no such man. Except the man who had the pauldrons upon his pauldrons.
"No. Was it the man with all the pauldrons? I think Guilliman took inspiration from him, though." It was true. Guilliman truly had many pauldrons.
"No, It Was That Guy That Beat All Of You With His Fists. He Was Also The Guy Who Out-Hugged Vulkan. It Was Funny To See. HAHAHAHAHAHAHAHAHHAHAHAAHAHAHA!" Dorn remembered now. It was funny. He added it to the list of things he found funny.
"I do now, father. But why have you brought this up? I was in the middle of building you a Father's Day fort. It is going to be a scale model of the Imperial Palace. Do you not like it, father?" Rogal asked.
"No, I Enjoy It My Centuri-Bear. But The Guy Who I Just Brought Up Is Still Alive And On His Way Here. With His Son, Sly Marbo." Rogal knew of the Hero of the 41st Millennium. He was given the Star of Terra a total of 47 times. He was very stealthy, but very loud.
"He is on his way, father? Why is he coming here? And would it not take weeks to get here from nearly all inhabited planets near here?" Rogal was confused. He did not like being confused. He did not have his glove to distract him from it. Unless…"Father, are they going to crash through the-"
Rogal was cut off by two figures crashing through his ceiling. That he built. When he still had his hand and pain glove. Rogal was mad that his roof was ruined. He would use that anger to make it better.
The Emperor noticed that the both were covered in the blood, guts, and viscera from demons. It seems that they had a productive day. "It Seems You Had A Productive Day, Sly And Slayer. Do You Have A Tally? The Scribes Will Add It To Your Record." Indeed, the scribes of the Imperial Palace had a tally for the Slayer in his head count. It was bigger than the number of times Leman used a variation of "wolf" as a swear stand in.
The Slayer popped an AI chip into the back of his helmet. After a few moments, a symbol appeared on his visor. "Greetings, Emperor. I am VEGA. The Slayer's headcount of today adds to one trillion, five hundred and fifty six billion, seven hundred ninety six million, four hundred and eighty four thousand, one hundred and sixty one kills. For daemons of the Nurgle variety. In the Tzeentch variety, there are-" The Emperor listened intently, memorizing them to pass onto the scribes later.
Much later…
MasterOfPlans: Lady gods, gentle gods, whatever Khorne and Slaanesh are,
RIP AND TEAR: HEY!
MasterOfPlans: I bring you good news! It is now Take Your Child To Work Day! So, not only is the Slayer out of the Picture, but Sly Marbo is, too!
Golden Boy: Well, if it wasn't for you, I might still have some more children to bring to work. Looking at you, slob.
Grandpapa Nurgz: Hey, that hurts my self-esteem. Not as much as your phantom itch, I bet.
[Bazinga]: BAZINGA!
So, you enjoy?