Standard disclaimers apply.
He couldn't remember meeting her. It was possible that he'd forgotten, but not plausible; he remembered much of his life—his father's death, his mother's grief-induced decline, and most things in between—but not the first day she came into his life. Simply put, Keiko had always been there. Naively, he, as a young boy, surmised that she always would be.
Her parents died the night before she was to exit the fifth grade. That he did remember. The official report said they'd taken a nasty fall, but he suspected they'd jumped and abandoned their only daughter. He never mentioned this to anyone but his best friend, of course—he would never intentionally hurt her.
He didn't want to see her go into a foster home, so he invited her into his mother's apartment, and there she stayed. Keiko helped his mother around the cramped space, running errands and taking care of chores when she could. He gave up his bed for her and slept on the floor without complaint. She tried to offer herself to the couch, but he refused; there were only two beds in the apartment, and he would sleep outside, in the cold, in the middle of the street, before he made her sleep on anything she wasn't meant to.
Things were like that for a time; a routine developed and settled. Their lives could almost be called ordinary. But then, as Keiko said, the his mother finally succumbed to grief, and then it was just them in the apartment. Seventh grade was just starting, and they were alone in the world, just the two of them. It hurt without his mother's kind smile there to guide him, without her eyes trailing after him and Keiko as they ran out the door for class. But they managed.
For a while, Keiko slept in his mother's bed while he slept in his own, but the fear of dreaming kept him up at night. Memories of nightmares tearing him out of sleep screaming for his father still haunted him, even if his mother had forgotten. Two months after the fact, in the middle of the night, Keiko appeared in the doorway of his room, swift and gentle like the summer wind.
She asked him if she could stay in his room for the night. When he began to shift, she rushed to amend her statement: she only wanted to stay in his room if he remained as well. And that was how it happened. They fell asleep on opposite sides of the bed, but woke up at dawn, his front pressed against her back, his arm wrapped securely around her waist. For once, it had been a dreamless night.