if he did killed Yin then everything that amber predicted or said would have been an error. couse the boy woke up, possibly with the dark yin inside her.

Hei will probably found another way to save Yin couse of the promise he made about being together, (“its true that he promise this to a lot of people and that he is not a man known to keep his word”) but also he is known to go against what everybody says and do what he things is right and find another way to finish the job.

Only question i can get is who is that yellow spectrum in Yin dream and in the last episode of the OVA… And why is he inside yin… “i want to think he is the black yim but its hard to believe couse he looks like a good boy giving people wishies, to yin and
to shion.”
Reading all this made me no want to kill my self lol…

and R3VOLV3R@ made me lough

When Hei finds Yin’s “spirit,” there are of course two of her (black and white clothes).

When he is seen walking off with her, it is her “spirit” that he is carrying, because her body is still back in that room.

What makes the most sense is that Hei somehow wished for the two Yins to be separated, and he is now carrying the spirit of the Yin he knows back to her body.

(Essentially, he plans to place Yin’s spirit back into her body.)

This makes the most sense because a Yin-look-a-like (in the coffin) steals the “souls” (or whatever they are) from the military men and then wakes up.

This Yin-look-a-like has a body and has the “evil” powers of the black-clothed Yin (at the very least, this Yin-look-a-like has the evil intentions of the black-clothed Yin, since she steals those souls).

I’m pretty confident this is what is occurring in the ending of Darker Than Black 2.

If you agree, you should probably include this answer as part of your post above because otherwise it is unlikely to get seen at the bottom of these comments (and the overall goal should be to answer the question of what happens at the end of Darker Than Black 2 in order to satisfy your readers).

I really hope this helps!