The name "Rubedo" refers to the philosophic beliefs of Karl Jung, who believed that the process of self-realization has three major steps, which he named using terms derived from alchemy, which he studied prior to developing his theories. These three steps are known as Negredo, the death of the old, perceived self, Albedo, the discovering of one’s inner identity, and Rubedo, the process of living a self-aware life.
666 is the number of the Beast (also called the Anti-Christ), a seven-headed emissary of the Devil in the Book of Revelation and alongside his power of the Red Dragon Jr. is set up as a demonic character superficially but lacks any such personality traits. However, the comparison to the anti-christ is fitting considering he was designed to produce the anti-wave of U-DO, a god.