Harry Potter was walking along minding his own business when suddenly he tripped over nothing and fell fifty odd years into the past without any sort of reasonable cause or explanation, but he was cool with it. He stood himself up and found himself face to face with Tom Riddle, who was, by sheer coincidence, the same age as him.
"Hi. My name's Harry Potter," he introduced himself. "I come from the future where you are a mass murdering Dark Lord hellbent on world domination. You murdered my parents and have been trying to murder me since I was a baby because a prophecy said I would destroy you. Let's be friends."
"Hello Harry Potter," Tom replied. "I'm Tom Marvolo Riddle. I created a pseudonym for myself of 'Lord Voldemort' by making an anagram of my name. I have already murdered people in my intention to take over the world, but, now that I've met you, I'm going to cast my plan aside and not become a Dark Lord after all. You see, I find you particularly attractive, and I can also sense that you have part of my soul inside you. You must be a Horcrux that I will unintentionally create sometime in the future. Because of this, I'm now madly in love with you. Let's go sleep together and live happily ever after."
"Okay," Harry agreed with a happy shrug, and the two walked off into the sunset together.
If only it were that easy…