Thats.... Actually a really tough question. I can't say I've read an incredible amount of manga, especially not futuristic ones. But, honestly I don't think Natsumi Kei's style would really work with Ciconia, I think its way too Umineko to be Ciconia, if I can express it that way.

So, I don't really have any idea of who would be cool to adapt Phase 1, but I'd love to see some side story material about the darker sides of the Ciconia world done by Yoshitoshi ABe.