Darker than Black 2 explained: did Hei kill Yin?
This is neither official nor sanctioned, but another interpretation from the arcana of the final episode of Darker than Black: Ryuusei no Gemini. I will not be like others, however, that will execrate BONES for their trolling, or curse them for what they have done to the franchise. I will simply try to explain things the way I understood them.
I personally saw the ending as decent: it wasn’t great or awesome, but it was quite solidly done. The episode affirmed, in a subtle way, that Hei loved Yin and vice versa. The point of contention is really whether Hei killed Yin. I personally don’t think that he did, primarily because in the final scenes there was a bifurcation of personalities: one Yin was black, and another was white. The White Yin was the one who asked Hei to kill him, whereas the black Yin stayed in the background. This made me personally reflect on Izanami as just a personality that branched off from Yin, especially because I just finished watching the particularly moving Kara no Kyoukai. The black Yin may be a male personality of Yin, and the white Yin is the Yin that Hei knew and loved all along. It is said that in the gate one gains something in exchange for something equally precious, and the return of female Yin to her own body and to Hei is paid off by the loss of her Izanami personality to another body, the male doll eerily similar to Yin and armed with her contractor-killing powers, as well. Hei’s gain of Yin is accompanied by his loss of Suou, a person who has grown valuable to him. With Shion’s ‘flawed’ world he lost his life; with Suou’s loss of memories she gained a new life in another world. The same can be said with July, who has once again become human in the world Shion tailored. It’s quite allusive to Fullmetal Alchemist with its idea of equivalent exchange, but it’s not altogether illogical.
All in all, it’s a decent ending.