Harry hooks up with a widowed Narcissa Malfoy during Post War (how is left as an exercise for the reader). This leads to them having a bunch of nights spent over the Harry's place since he has no one around his place other than Kreacher.
A few months later Ron puts his foot in his mouth and needs to crash on Harry's couch. This of course comes right at the time when Harry and Narcissa had planed to make Grimmauld Place a den of debauchery. Instead of postponing or calling a raincheck, Narcissa proposes Malfoy Manor. Harry has trepidation due to the bad experiences during the war, but muddier heads prevail and horny wins.
They arrive at the manor and begin their path of debauchery. From the unrobing in the foyer to stopping by the kitchen to pick up some snacks and water to re up their electrolytes, they systematically work their way through the manor. (Feel free to insert scenes of them playing with the manacles and pillories in the basement if that's to your taste).
Finally they are down to 3 untouched rooms. One is Draco's childhood bedroom, next to that is Malfoy gallery, and finally the Master bedroom. Once Harry hears Draco's bedroom he care little of the others and near drags Narcissa into it. Once that is thoroughly defiled Narcissa insists that they refresh in the ensuite bathroom to the master bedroom. Of course there is a mess left in their wake as they finally decide to crash in the master bedroom a few hours later.
Now awake and refreshed, Harry is aware he probably needs to be responsible and an adult but finds the prospect banal as he lays and basks in the gentle attention of his lover. Narcissa noticing his reaction to her ministrations pulls him out of the bed after grabbing her wand.
Before Harry or the occupants of the room can react, Narcissa swishes her wand and nearly all the paintings on the walls are covered or frozen. Harry can't help but gawk at the long curved walls covered with hundreds of paintings of long dead Malfoy's and the single large ottoman in the center of the room. Everything in the room speaks opulance, but none of that holds Harry's attention compared to the apoplectic screams of Lucius Malfoy.
Except it wasn't the convicted and executed Death Eater present, but instead a portrait of the man. His lucious locks and serpentine cane contrasting to his decidedly Weasley coloration as he screamed obscenities at Narcissa. Narcissa takes in the vitriol with a cool countance that Harry has never seen and hopes to never see leveled at him. With a sharp bark Narcissa cuts off Lucius and starts to deride him.
Harry is gobsmacked and just watches on as Narcissa begins to ridicule Lucius, his manhood, his line, and his worth as a husband. Before he knows what's going on Narcissa has Harry on the ottoman and begging and pleading Harry to breed her without the help of potions like a real man. Harry just goes along with it and just tries to hold on for dear life. Meanwhile Lucius is raging in impotent rage.