Well I finished watch Darker Than Black: Ryuusei no Gemini like... maybe 1 month ago? I finished when the last episode of the season came out. :) To me... this movie is probably just a 7 or 8? It doesn't have the best plot ever. It's about a 13-year-old Eurasian girl, Suou Pavlichenko, becoming involved with the Darker than Black world after her father and twin brother, Shion Pavlichenko, was apparently murdered. Suou soon starts traveling with Hei along with July and Mao, who actually didn't die and is now in the form of Suou's flying squirrel. lol. Suou eventually falls in love with Hei. A 13-year-old girl falling in love with a twenty-something-year-old man. wow. lol. But Suou doesn't realize that. Hei and Mao does. :)
In the end... well. You are going to find that out yourself. :) hehe.