The official website for DARKER THAN BLACK: Ryuusei no Gemini [流星の双子] has been updated with a trailer for the anime series that is scheduled to air this coming October.
The synopsis of the sequel according to ANN:
The story continues two years later and follows the main characters Hiei and Yin on the run as they encounter a Russian-Japanese girl named Suō Pavlichenko.
Source: DARKER THAN BLACK 流星の双子 via ANN
I only managed to watch the first season halfway, so I guess I have to complete it soon before season 2 comes up.
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There is another trailer (1:30 min approx.) and it’s about the new girls, Suou Pavlichenko.
http://www.youtube.com/watch?v=lwF2WD0kjeI
Season 2 rocks. I love the plot