Here's one I came up with whilst having a pint at a Spoons...
The Dark Lord was sitting in his throne room, his mind rushing as he reviewed his plans, his Agents in fear of him, knowing that one wrong move could send their Lord and Master into a foul temper.
This Dark Lord was the third Dark Lord in the past century, but unlike the other two, this one wasn't dark because of Albus Dumbledore.
He turned to the Dark because of Hermione Granger.
Hermione Granger, the love of his life.
Hermione Granger, the one to who he had lost his virginity.
Hermione Granger, the one who disappeared.
He had last seen her the morning after the Battle of Hogwarts when they had slept together, Harry after seeing Ginny and Neville kissing each other, and Hermione after yet another argument with Ron, mere hours after kissing him as though it was about to be made illegal.
In reality, Harry should have realised that he and Ginny had been over since Dumbledore's funeral, and because of that she was a free agent, but the red-eyed had beast came out and he had punched Neville, calling Ginny a slapper and leaving the Great Hall.
Their night had been wild, with Harry's stamina outlasting what Hermione had told him would be the average sexual stamina of the male of the species, but when it came to morning, Hermione had told him she had needed to visit Madam Pomfrey about emergency contraception, as in the lusts of their passion, they had forgotten the Sexual Protection Charm.
But according to Madam Pomfrey, she had never appeared in the Hospital Wing.
Upon hearing this, Harry had run into the Great Hall and, gathering the Order of the Phoenix, organised a search party of the castle.
That turned out to be a useless idea, so, upon the advice of Kingsley Shacklebolt, an all Britain search for Hermione had been ordered.
That search also turned out to be useless. So Harry, thinking the worst, assumed that she had been kidnapped by a Death Eater who had not been captured.
And he snapped.
He visited the home of Draco Malfoy, Malfoy Manor, and interrogated the blonde Slytherin. And Malfoy named names of Death Eaters, Snatchers and Death Eater sympathisers, albeit with a bit of an inducement...
...a Cruciatus or six.
Not long after the Aurors visited Malfoy Manor, what Aurors that were alive following the takeover of the Ministry and the Battle of Hogwarts, and Malfoy told them who cast the Cruciatus on him.
Not that it mattered though, as the Aurors knew that they were dealing with the man who killed Voldemort.
One by one the Snatchers, Death Eater sympathisers and Death Eaters that had evaded justice, or were yet to be captured by the Aurors, all died, all of their deaths being the same way, a Killing Curse.
And then the Aurors struck.
It was a cold day towards the end of February 1999 and the day that Harry spat on the Light for the last time.
Learning from a tip-off that Harry was going to be in Diagon Alley visiting the recently reopened Weasley Wizard Wheezes, they tried to arrest him. Obviously, following procedures wasn't enough though as Harry had managed to whittle their numbers down, with only 2 Aurors remaining standing when Harry saw a woman with bushy brown hair in the Alley walking towards Gringotts, carrying a baby.
Getting distracted, he found that he had been hit by a Cutting Curse. However, that didn't phase him, as he took out the last two Aurors without a hitch.
Running towards the woman who he had seen entering Gringotts, he watched as she entered the bank. Unfortunately, though, it had turned out not to be Hermione, but Harry had received a shock anyway...
...his Account Manager told him that there was a new Potter Heir, a son between himself and Hermione Granger.
Leaving the bank, he realised that it had been 9 months since the Battle ended, and with that, he worked out one thing. Hermione had deliberately left him after sleeping with him because she was ashamed that she had slept with him.
The years passed, Harry turning Dark by the day, sending people all over the globe to find Hermione, to bring her and his son back, and at the same time taking over the Wizarding World, personally killing those who opposed him.
All until the Ministry, Hogwarts, Gringotts and St Mungos were all under his control.
The Light took casualties. The Weasley family were the first to go. Bill and Fleur leaving England for Fleur's native France in order to avoid swearing loyalty to the new regime with Bill's brothers Charlie returning to Romania and George leaving for America with his fiance, Angeline. On the other hand, Molly died of a curse that Bellatrix Lestrange had cast on her during the Battle of Hogwarts. Percy in a 'freak' accident in the Ministry involving a dodgy cauldron. Both Ron and Ginny were killed for refusing to submit to the new order.
Then the Longbottoms were eliminated. Neville, ever the Herbologist, left a series of booby traps to stop the advancing Dark Lord, but those were swept away. Neville's wife Hannah, killed protecting her infant son and Augusta, dying from her injuries as a stray cutting curse from one of the supporters of the new regime. Only the son was safe, given to one of Harry's supporters to look after.
Susan Bones and Megan Jones tried to integrate themselves into the new regime in order to help the resistance, but they were executed for their betrayals, as they had tried to manipulate him into sleeping with them.
But the Muggleborn on the other hand, supported the new Dark Lord as he had stripped the oppression against them that the Purebloods of the previous regimes had set up.
But that was still nothing to bring Hermione back.
The ICW wasn't bothered with the Dark Lord Potter's takeover of course. As long as the Secrecy laws that had been put in place were not broken, they didn't care who was in Government at any time. Pockets of resistance formed across Magical Britain, but were swiftly dealt with by Agents, careful not to break the Secrecy laws.
It was only due to good fortune that one of Harry's lieutenants, a Gryffindor who was two years behind him named Tony Smith had received word from an informant three years after the Battle of Diagon Alley that Hermione Granger had been spotted in Wellington, the capital of New Zealand, or so they had thought.
Obviously by the time Agents of the Dark Lord Potter had got to Wellington, there was no sign of Hermione Granger or her family. Several Agents were punished upon the Dark Lord hearing the news they had brought back, with only Luna Lovegood being the only one to escape punishment. The reason he didn't want to hurt Luna was simple - she was the only person alive that was still a friend to him.
The takeover of Hogwarts five years into the new regime was the easiest, with the teachers all swearing loyalty to the Dark Lord. The main target, however, was The Book, a register of all magical children that had turned eleven in the whole of Europe. The book that would eventually show the location of his child.
That takeover proved fruitful, as, upon the eleventh birthday of his son, the Dark Lord dispatched agents to the location of one James Sirius Potter, son of Harry Potter and Hermione Granger.
Waiting in his throne room, the Dark Lord watched as two of the Agents dragged Hermione Granger from where she had been hiding out, a little village outside of Newcastle. Looking at her, he could see that she had been roughed up. Leaving his throne, he knelt down beside her and looked at her face, her chocolate brown eyes bringing back memories of that night of passion.
Raising his wand, he cast a Cruciatus Curse at the two Agents. "I said bring her in, but I expressly ordered you not to harm a hair on her head," he said, annoyed with the two Agents who had brought her in. "Where's my son?"
"Dead my Lord. Granger wouldn't surrender him." The Agent who had been first to recover from the curse being cast at him. "Stebbins had to knock Granger out and then when the boy hit him, I reacted."
Harry stood up, towering over the Agent, fingering his wand. "Reacted? Reacted? How about this for a reaction. Avada Kedavra"
Both Agents fell down as the Dark Lord cast the spell at them. Picking Hermione up, he carried her bridal fashion to his private quarters, his magic expelling everywhere. Heading into his bedroom, he lay her on his bed, heading into the bathroom in order to run a bath for the one person who he loved above all, pouring Healing Potions into the bath.
Transfiguring Hermione's clothes into a bathing suit, he placed her carefully in the bath. As he did so, Harry started crying.
He had started crying about what he had become, crying about the loss of a son that he had never got to know, crying about what his parents would think about him.
And he cried for Hermione. How she would never be able to see her son pass his OWLs with straight O's, become star seeker of the Quidditch team, become Prefect and then head boy. How she would never be able to see James Sirius be able to graduate Hogwarts, get married, and be able to have a child of his own.
Watching as Hermione's wounds started to heal, he left the bathroom, heading to his study. Entering the study, he reached for the Resurrection Stone that he had kept in a locked safe, keyed only to his blood.
Before he started the process to be able to talk to somebody close to him who was dead, he placed the Stone on the desk nearest the safe. Instead, he reached into the safe for a Potion that he had brewed only one vial of, one that he did not want to use at the time of creation, but would be the only option if the worse had come.
A Potion that would kill him, and only him.
Unstoppering it, he peered out of his study towards the bathroom to see if Hermione had woken up. Seeing that she hadn't, he pulled his diary out from the safe and, leaving it on the page of the recipe for the Potion, he drank it, knowing that he didn't want Hermione to see him weak.
Eventually, life left the Dark Lord Potter, and with it, the end of the Potter line.