Disclaimer: this is, at most, a loose translation that I've tried to make sound as natural as possible in English.
(1) interview with Okumura-sensei, posts 20-21
From the "Maker Oudan Anime Guide" (a magazine)
At the very end, the twist of "copying the earth" was really surprising.
(Okamura) Shion has the power of copying things. After we started with him copying small objects, I guess you could say that we were thinking "So, what can he ultimately make a copy of?" when we arrived at that.
And where is the copied earth located?
(Okamura) When it first appeared, it looked like a moon, but it ended up moving further away, didn't it? After all, physics dictates that when objects are close to each other, the effects of gravity will bring about disaster.
Then, are lots of people living normally on that earth?
(Okamura) That's a good question. The copies made by Shion are all different to their originals in just one aspect. The copied earth is one without the Gates. Everything else is the same.
In the end, what finally became of Hei and Yin?
(Okamura) What became of them indeed? (lol) Yin certainly looked like she was dead. As for Hei...well, the BK201 star seems to have remained.
Does that mean we can expect a third season?
(Okamura) No. I've done everything I wanted. I always thought of this as the end, which is why we've revealed background information bit by bit.
Then, all that's left is the Gaiden. Chronologically, how will it be related to the two seasons?
(Okamura) The second season is set two years after the first, and the Gaiden about a year before that. If we'd included Hei's story in the second season, we know that the focus would have be lost, so splitting it up became very easy.
Please tell us what we can look forward to in the Gaiden.
(Okamura) The first Gaiden is about "Hei's honeymoon with Yin" - we hope you'll enjoy that. What's happening with Yin will slowly be revealed. Also, there wasn't much typical "Hei action" in the second season, so we'll be putting more of that in too.
(2) summary of what we can deduce
■Events that happened before the start of the second season <= the contents of the OVA
・What happened to Yin, making her able to suck up souls.
・What happened to Hei, and how did he come to split up with Yin and end up looking for her. (He knew that Yin had changed.)
・Mao came into the service of Madame Oreille (Mao's server is probably being managed by her)
・July met Yin somewhere, and came into contact with Madame too.
・Madam, Shion and the twin's father worked in cohorts with each other.
・Shion used his power to copy earth and humanity (the memories of the copied people are preserved/maintained in the large meteor fragment).
・Shion's obeisance was not that he lost control of his legs, but that his body became weak.
・The real Suou had already died, and the current Suou is actually a copy of Shion, made with the latter's ability.
・July is an important spy for both MI6 and Madame (though his real allegiance is to Madame).
・On the new earth, July is no longer a doll, and retains his real memories from the original earth.
・The copied earth is moving away from the original, making sure that it can't be affected (by anyone) from the latter.
・The Mitaka Documents seem to be memories retrieved (through the ME) and put together from the Stargazer (Hoshimi-sama)
・The Yin look-alike at the end, which sucked up the souls of the CIA goons, was "the great calamity" predicted by the Mitaka Documents.
・At the start, Hei worked on commission for both Madame and the CIA (allegiance with Madam), with his reward to be information on Yin's whereabouts (though Madame didn't tell him).
・The Dr. Pavlichenko that Hei killed was a fake, and his death was also planned.
・Madame had Hei look for the meteor fragment in order to bring Hei and Suou together.
・Madame and Shion's plan was to entrust Suou to Hei, leading him to Tokyo (doubling as an experiment testing that the fragment could be used to hold memories)
・Section 3 is 'the Syndicate'. Outside of destruction, their goal was to prevent the meeting of Izanagi and Izanami.
・Shizume was the one who released the info on Hazuki and Sawasaki. He also killed Sawasaki.
・The Magician survived - the person the Shizume killed was someone that he'd changed places with.
・Shion had been planning this for a while, so Amber knew it from the "Memory of the Future" and passed it to Hei through Misaki.
・The Syndicate was destroyed, and America occupied Japan.
・Section 3 failed to hinder Madame and Shion's plan, and their remnants (Golgo, Misaki, Madame, Mao et al) joined forces, forming a new origanisation, which would then on be known to people as "The Syndicate"
・Why was Suou so emotional despite being a contractor?
・the whereabouts of Hei and Hazuki.
If you have any differences or supplements, post them.
Time taken: approx. 1 hour on 2010-05-27