is a Japanese manga series written and illustrated by Rei Hiroe. It has been published in Shogakukan's Monthly Sunday Gene-X since 2002, and ten collected volumes have been released so far. It was later adapted into an anime television series by Madhouse, that aired from April to June 2006 for twelve episodes. A second season, subtitled "The Second Barrage", ran for twelve weeks starting on October 2, 2006. A five volume original video animation series, titled Roberta's Blood Trail, was released from July 2010 to June 2011.