Disclaimer: I own nothing of the rights to Harry Potter or Doctor Who.

A/N: Here is the first entry in Leicontis's Laboratory, a dumping ground for random prompts, challenges, ideas, and story bits that pop out to me. I had been intending to wait until I had more material collected, but my main story (Umino Iruka and the Will of Fire) just hit 100 followers and I had to celebrate.

As with my other ideas fic The Kunai Pouch, anything I post in this fic is up for adoption or use, in whole or in part, so long as credit is given and you let me know so I can get to see my idea developed. There are some guidelines I'd prefer to see followed if you do build a fic on my ideas, but I'll put them down in the end A/N.

-Christmas 2006-

The Second British Blood War went badly... very badly. The Dark forces had too much popular support and not enough popular opposition. They had too much financial and political power. They used tactics no person with a functioning conscience would ever touch. They were winning, crushing all opposition, and victimizing countless others. Then they made a mistake.

They killed the woman Harry Potter loved.

Soon, to their detriment, they found that Harry Potter truly was the Dark Lord's equal, as prophesied. He was equal in power, equal in talent... equal in hatred, equal in cruelty, equal in ruthlessness. Potter abandoned the gentle, capture-focused tactics of the Light, passed over the harsh pragmatism of the Gray, and began destroying his enemies with the vicious cruelty of the Dark. He copied his enemies' tactics, striking at vulnerable targets, wiping out families while their patriarchs were away serving Voldemort, visiting the same horrors on the Death Eaters and their supporters that he and his had suffered for so long. In his grief, he was determined that all those he held responsible would share in his pain.

Now, over fifteen years since his reintroduction to the wizarding world, he sat alone in a cheap room, drinking to numb the pain as he remembered happier times, paying only minimal attention to the program on the telly - something with a flying phone booth and spider aliens. He watched with approval as the hero destroyed the invaders, protected the Earth, until one snippet of conversation consumed his entire focus.

"I don't need anybody."
"Yes you do. Because I think sometimes you need somebody to stop you."

The woman's statement crashed through the drunken haze, through the pain, through the years of blood and terror and hate, and straight to the most wonderful and painful memory of all - his love. A handful of words in a television Christmas special changed everything.

How would she react to what he had become? Harry's mind easily conjured images that cut deeper than any wound he'd received in years: Her shock, horror, disappointment, disgust - he deserved all of them. He had become the very thing he hated most, and even worse, he didn't think he could reverse the change. It wasn't as if he hadn't tried already, tried again and again to take the high road, to be better than his enemies, but eventually he'd slip again, and with nobody to pull him back he'd become a monster once more. His "upbringing" by the Dursleys hadn't taught him anything about compassion, or kindness, or restraint, or mercy - only cruelty - and with the loss of his love he lost the ability to even see the line before he was far past it. Finally, he understood why he'd failed to be better: He needed help, and not from just anybody. Only one person could pull him away from the darkness. His heart could only be returned by the woman he'd given it to, but she'd taken it with her to the grave.

He needed her, and only now did he truly grasp how desperate that need was. There was no way to bring her back; he'd learned enough Necromancy in the past few years to understand that the gates of death only swung in one direction, no matter what anyone had ever tried. Joining her was out, too. Giving up just wasn't in his nature, and even if it was, he doubted that his "next great adventure" would be anything like hers after all he'd done. What did that leave? His alcohol-fogged mind cast about randomly, conceiving and discarding ever more absurd ideas, until it latched onto a memory of an hourglass pendant on a gold chain, and a bird in a bell jar. If he couldn't go forward, or bring her back, then all that was left was for he himself to go back - back to before everything went to Hell. Back far enough to save her, and if he was really lucky, to save himself as well...

A/N: And here you have my generic opening sample for my "Someone to Stop You" Challenge. I deliberately left the love interest's identity undefined, as I'm not super-attached to any particular pairing in the Potterverse (save possibly for Luna with Whoever Luna Wants).

The basic idea is as follows: Harry was in love. His lover was killed by Death Eaters, and something inside him broke. He went dark in a big way, and replaced the kid gloves with spiked gauntlets. Eventually, he realized that he'd become a monster, and that he needed his lover as an anchor to sanity and morality, sort of a Jiminy Cricket to his homicidal Pinocchio. Cue standard do-over-style time-travel story, with a jaded killing machine trying to play the role of naiive schoolboy and re-woo the person he loved, while dealing with such conflicts as "going by mental age, any attempt at a romantic relationship right now would be seriously creepy and messed-up" and "I don't want to build a relationship on lies and secrets, but I also can't tell her the truth about my future-past yet for fear of scaring her off".

A plural relationship really doesn't work with this idea (at least I can't see any way to make it work), so I strongly advise against it. The strongest candidates for Harry's love interest would be Hermione (very steady moral compass) and Luna (gentle and compassionate), but any character that could plausibly both end up romantically involved with Harry and act as a strong moral anchor would work.

Inspiration-wise, I think this came in part from the title-providing Doctor Who quote and in part from a fic whose title and author I can't remember, but which had Harry time-traveling to save his loved ones but avoiding developing a connection to Hermione (his lover from the previous timeline) out of shame for the fact that he was a killer. I remember it had him carrying out a big purge one summer, scaring the pants off of everyone, revealing the truth to Hermione later, she freaked out (not unreasonably) and left him, only to reconnect years later after one of her university friends brought up the Trolley Problem.

My general guidelines for fics using my ideas:

1) No incest or otherwise inappropriate pairings (like teacher/student or pairing an adult with a much younger child), and absolutely no sexualizing young teens and preteens (yes, I know it happens in real life, but it's still not something to promote, and stories that have thirteen-year-olds and even younger children engaging in intimate activities are a total no-go).

2) No SIs or OCs in central or major roles unless said role is necessary to the story and no canon character can plausibly fill it. For an OC used well in a major role, see Barchoke in Harry Crow. Examples of OCs and SIs being used badly in major roles are sufficiently abundant that I'm confident you can find one if you look hard enough. Worst case, dig up the Star Trek fanfic that gave us the name "Mary Sue" for an extreme example. Or read My Immortal, if you enjoy suffering.