This arc is different in a fact that the entire story and its background is so far into the future.
Most of arcs occur between 9600 ~ 9800. This arc is way far into the future in 12xxxx. In other words, this ac is pretty much standalone and can be read without having read any of stories of Two Clusters.
The universe is being ravaged by unknown entities. Humans are on verge of total annihilation. But, somewhere deep in a nebula, pirates rise up.