I loved Darker than Black season 1. I thought the characters, atmosphere, and story were all spectacular. Then I watched season 2. And boy, was it different. Virtually every single thing that I loved about season 1 was changed beyond recognition. The ending was so terrible and left me with so many questions that I literally stopped in the middle of my day that and wrote a list of complaints that I had about season 2. I was therefore incredibly happy when I began the first episode of Gaiden and could immediately tell that it was going to be a return to form for the anime.
Right from the beginning, you'll notice that the art style is back to how it was in the original series, just with improved quality. This works wonders in recapturing the nostalgia that many feel for season 1: it just feels right, like the creators are acknowledging that they messed up with season 2 and now they're going to give us what we actually wanted all along.
The music is great, especially the ending, but honestly I would be hard-pressed to recall any moments where I specifically noticed the background music, just because I was always focusing so much on the action onscreen and the dialogue that it never stood out to me.
The story is basically an explanation for a whole bunch of nonsense that was thrown at viewers in season 2, and a well-needed one at that. Season 2 makes absolutely zero sense without this, so it functions exactly as it should. That isn't to say that this is all it does, though, but it's hard to go into detail without spoiling anything. I'll just say that the story is back to being Badass Electric Batman Hei and Yin versus the syndicate, instead of being Magical Girl Suou and Alcoholic Hei versus a bunch of trope characters.
Character development is where this OVA really digs in deep and hits you hard with the feels. Hei and Yin are on the run from the syndicate together, and all they have in the world is each other. It's all of the drama and relationship development that you were itching to see in season 1, and most of the focus is entirely on them. This leads to some very emotional scenes, and I'll admit that I even shed a few tears over this anime.
Overall, I highly recommend Darker than Black: Gaiden to anyone who enjoyed the first 2 seasons of the anime in any capacity. Even if your opinion is the exact opposite of mine and you disliked season 1 and loved Ryuusei no Gemini, you'll likely still appreciate how Gaiden smooths out the story of the second part. I cannot imagine why any fans of season 1 or season 2 would not enjoy this OVA, unless you're only invested in the new characters introduced in season 2 and nothing else.
