The narration of the story in Red City is being conducted in dual number. Not singular number, as in traditional narrative cinema, nor plural number as in some documentaries. Dual number hasn’t been used in the language of cinema. In fact, it doesn’t exist in most modern languages anymore - except for some traces of it (i.e. both rather than all, neither rather than none). It was used in ancient Greek, Sanskrit, Gothic and many other dead languages. 

The mechanism of dual number narration is telling a story by following a central pair of characters, rather than following a single central individual character. And accordingly, you have a few supporting pairs of characters interacting with the leading pair, rather than having a few supporting characters interacting with the leading one. The whole point of doing this is to highlight a central truth of life. That no one stands alone. That it is through each other, not through individualism, that we get any awareness of ourself. And that in life - regardless of whether we are conscious of it or not - our paths are always coupled and entangled with other people’s paths. And our actions affect their lives and their actions affect our life, directly or indirectly. It’s a notion of interdependence of people, and a pre-existing solidarity hidden deep within the very nature of human societies - even of the most inhuman ones. That’s one of the main points of the film, and the unconventional narrating style with which the story of Red City is told highlights that very point.