First, as we learned last chapter, the car they're in now is the same car that the guy was driving when he hit her. It's also the same car that Kouhei was gawking at as a kid, and went outside to get a closer look at. It was apparently hanging around in front of his house - it's shown more than once going by or stopped out there. And it took off when he went outside, which was when he stepped out into the street, to watch it as it drove away, and almost got hit. And she's the one who pushed him out of the way and saved him.
But she says she "chose" him.
I noticed this time through the chapter, because I suspected it and was looking for clues, that it's strongly hinted that she was already dead then - that he was actually saved by her ghost. After she knocks him out of the way - while they're still on the ground - she berates him for almost getting hit, then says "Do you want to die as well?" Like she was asking if he wanted to die in addition to her.
And he has a repressed memory of her corpse.
Maybe he saw it happen, and the driver knew it, and that's why he was hanging around the house? And maybe ghost-Chiaki was also hanging around his house, because she'd already chosen him at that point to be the means to her vengeance? So she didn't just happen to be there - she was deliberately there. And that ties in with him commenting when he was retelling the story that he thought it was odd that the girl he couldn't remember was out in the pouring rain when it all happened. She was there because she was watching over him, and the rain wouldn't matter to a ghost.
That's all guesswork though.
And meanwhile, back at home, the cop and Chiaki's sister have teamed up and started looking for the guy Chiaki apparently just killed. I suspect they're going to show up pretty soon - maybe even next chapter.
And I wonder if they'll be able to see Chiaki.[\SPOILER]