honestly Atsushi is doing something good for once. he's now gonna lead Keita to Aihara and finally he'll have his revenge.
So Natsumi has a history of murder before? it seems it was self defense. I can see it got her so depressed she clinged to someone as abusive as Keita and his constant beatings convinced her that its her punishment for doing such things isnt it?
I can see the ending. Keita'll probably have a big fight with Aihara. they'd both be bloody and almost dead. probs Keita dies (hopefully horribly). Atsushi survives somehow, gets convicted. Natsumi survives, gets convicted maybe. Aihara's fate, I think he'd die before the cops come.