[ch133 to 136, click on thumbnails to enlarge the pics].
As everyone must [or not] remember, these doodles are for the Memories in the Rain 2 flashbacks, with Rukia killing Kaien [I hope that's not a spoiler anymore XD]. Those are very sad doodles... let me get to my point.
You know, seeing all this black made me think about the black page Kubo used at the end of ch56, when Rukia was taken away and it left Ichigo in such despair. I remember that right after that, Ichigo had suicidal tendencies, as pointed by Urahara - he didn't want to be saved, etc.
Then you see that despair again in Rukia's doodles - Kaien is her moon, then it clouded to finally disappeared - and there was no one anymore once she tried to reach that light.
Interestingly enough, Rukia is herself like a Moon, she became that light for Ichigo... and Ichigo became a dazzling sun, returning light and life to her right in ch01, allowing her to glow like a moon - that needs the sun to reflect the light. But, unlike KaiRuki that was bittersweet because it was all one-sided, the mutuality in the IchiRuki relationship allows her to be the light of that special person now.
And now, we have yet again those black pages for Ichigo who just lost his identity. I mean, considering that Kubo said that Rukia was Ichigo's light, of course I think she will have to play an important role - later on, when she'll be healed. Those black pages show utter despair, but those always get healed - that is one theme for Bleach.
As Annie told me, it looks like the Moon is, in Kubo's mind, the one thing that lights the path of someone.