BakuhatsuSeigi said: OBJECTION! Clearly, main character is not always singular. Case and point. Giratina and Shaymin. Latios and Latias. I rest my case.
COUNTER-POINT!
Adding all three of them to the picture would clutter so small a pane. The artist probably decided Darkrai was the one who should've been featured the most.
Never mind, the entire debate is pointless. The picture is as it is.
Without having seen either of the movies of 2007 and '08, may I suggest that Darkrai is relatively independent from Dialga and Palkia, who would undoubtedly be dual. Given the title, either Dialga and Palkia are attempting to suppress Darkrai, or Darkrai is attempting to quell a scuffle between the other two. In either instance, Darkrai is one party, Dialga and Palkia another. So, since the movie focuses on the former party, Darkrai is depicted on its own.
Now, space may well be enough reason for Shaymin and Giratina, but since they're both depicted, I'd expect them to have more of a duality to them. This then brings to mind about Lucario not including Mew, but Mew seemed a bit more like a target, and Lucario's scenes tend to be disconnected from Mew overall, more focusing on his time with Aaron or on his own.
