I'll keep this short: Anyone who is a fan of Darker than Black NEEDS to find a way to watch these 4 episodes; they are crucial to understanding so many things about the series, including several things that didn't make sense in season 2, the relationship between Hei and Yin, and Hei's character development.
The OVA bridges the gap between seasons 1 and 2, explaining what happened to Hei and Yin during that time, and not only is this information vital to the plot, it is incredibly entertaining. This OVA is 4 episodes of pure awesome, as we finally get long awaited closure about what Hei and Yin meant to each other and how Yin "evolved". There is no comedy, no side arcs, no anything; just 100% plot, and for a story I have become so invested in, I like it that way.
In case I didn't make it clear the first time, fans of the series NEED to find a way to watch these episodes, because they are both fantastic and important; I might have enjoyed them more then certain parts of the original series.
