Darker than Black 9-10 actually features the most incidental usage of the setting so far. Really it’s about the clash of two worlds coming together. Alice and Misaki are friends, but one is a gangster’s kid and the other is a cop’s kid who becomes a cop herself. Shenanigans occur.
Besides finally doing something with Misaki other than having her be the Clousseau to Li’s Pink Panther, this arc thematically supports the idea of the two worlds of the everyday and the extraordinary clashing. It implies that if one is entrenched too far in one’s own world, then yes indeed one is not going to be able to interact with anything else. The hint would seem to be that to find a kind of respite from the shit he goes through, Li is going to have to stop acting as a hitman/gofer for whatever shadowy organization employs him.
That’s seriously just about all I have to say about the arc. Hopefully the next will provide me with more to talk about.