The Death Stalk Unit is a group of four heavily muscled creatures (formerly humans) that are controlled by Iris. In the manga, they are four scientists, members of Millefiore's Research Facility, that have experimented on themselves to impress their assistant, Iris, and their object of affection. As they experimented more and more, they turned into mindless monsters that only heard and obeyed Iris. The anime takes on a more moderate view, as the Death Stalk Unit were not formerly human, but artificial creatures. They were monsters created by the four scientists, who decided to experiment after being encouraged by Iris. The first prey of the Death Stalk Unit was these four scientists who created them, as Iris betrayed them.