A genius mad scientist once bred a special flower in his quest for eternal youth and immortality, implanting the seeds of this "Premier Rose" in human beings. Housing roses inside their bodies granted the human hosts not only various benefits, but also various side effects, including the need for the roses to feed off of victims. The majority of the test subjects, "Black Roses," were used as living weapons and kept under control by their creator. One subject of the experiment was dubbed a "defective failure" and hidden away.

Claudia the "Rose Witch," also called a "Crimson Rose," normally does not need to feed on humans and only does so if she loses her self-control. When the Roses' creator disappeared five years ago, the organization conducting research swiftly rebranded as "Red Rose." Brought out of the shadows, Claudia became Red Roses' primary means to eliminate the suddenly untamable Black Roses.

Guarded by the "Thorn," Wilhelm, who shares a blood covenant with her—and working with a special division of Red Rose named "Crimson-Shell"—Claudia must survive betrayal by a suspected traitor within the organization, as well as discover the truth behind a "Jet Rose" who may be leading the Black Roses.