Darker than Black is one of those rare series which is consistently better than it probably should be. It has all of the elements necessary to be a run-of-the mill series about super-powered agents, terrorists, and hoodlums, yet somehow it puts them together into two-episode stories which carry a heavier impact and sharper edge. Lurking behind all of the super-powered antics, bloody violence, and intrigue is one of the year's better series.
Though events continue to play out in two episode mini-arcs, episode 13 also marks the beginning of the series' first overarching plot. With the introduction of Evening Primrose the series now has its first recurring antagonists (although one of the bad guys from the first half of the series does also resurface and continue to be a pain in the butt for Hei) and, finally, a sense of a greater purpose to many of the events that play out, although the direction they take may be somewhat surprising and the truth about who the ultimate bad guys are may be a matter of perspective. The Evening Primrose arc also finally explains in more detail what happened at Heaven's Gate five years earlier and, with its last regular episode, explains what happened with Hei's Contractor sister Pai (and that truth should definitely be a surprise).