ANN has an interview with BLOOD-C's director, Tsutomu Mizushima, and screenwriter, Junichi Fujusaku.
A few snippets--
ANN: This project is defined by the presence of CLAMP, and that's how the show is being sold, even in the title – how much input did they have on the story? How would you define CLAMP's impact on what the show is?
TSUTOMU MIZUSHIMA: I can definitely say that Blood-C is a strongly CLAMP-flavored project in many ways, both story-wise and visually, starting with the character designs. CLAMP's style and sensitivities permeate the entire series in every way.
ANN: How eager were you to reinvent the characters? Having written Saya for years now, were you nervous at all about remaking her personality as radically as Blood-C does?
JUNICHI FUJISAKU: I change Saya's character setting in each of her incarnations, which is always an enjoyable process for me. Saya singing songs, being a meganekko (glasses-wearing girl) and her hairstyle are all features coming from CLAMP.
ANN: What creative challenges did you run in to while writing Blood-C? What was the biggest challenge for you personally on this series?
JUNICHI FUJISAKU: For Blood-C, Ohkawa-san from CLAMP is taking care of the storyline for each script, and I dramatize the fight scenes. Ohkawa-san's dialogue has a very distinctive style, so I carefully avoid any intervention that would eventually spoil the final result.
[Full interview at ANN]