You hit him with your car.
To be fair, you hadn't meant to. You'd been backing out of your driveway, when something flashed blue behind you, and something else collided with your back windshield. You'd immediately gotten out and run around to the back of your car, only to find an unconscious young man in a- now dirty- suit lying on the concrete.
Thankfully, he'd lived. You apologized a hundred times over after he'd woken up, but he didn't seem to remember being hit. Or anything before, for that matter. The most he remembered was his own name- Five. An odd one, to say the very least.
So you'd let him live with you- said it was the least you could do for him, after hitting him with your car.
Now, several months later, he's still with you. You've been posting ads in the newspaper, and putting up posters, saying you'd found him, but no one seemed to know who he was. You promised him you'd find someone he knew before- you still felt shitty about the incident- but he'd told you he was content staying with you.
And he was, he decided. Whoever he had been before, they'd fucked up his mind. Everything felt achy, up in his headspace- and he could clearly see he'd been stressed before he forgot everything by the bags underneath his eyes.
The both of you developed a routine, living together. You had a job that paid the bills, and he had nothing but time. So he picked up on a few skills- a few things he enjoyed, actually. Gardening was one. He also learned to cook- not well, but he tried. And he read. Lot's of history books, books about past wars and monarchies and what not. He didn't have much else to do.
And so, the days went on like this- you'd leave in the morning, and come back in the afternoon. You worked from ten until six o'clock, Monday through Thursday. It was... Peaceful. Sure, he was restless, some of the time. But still, the normalcy of the routine was pleasant.