Chapter 4 is titled "Peeping Tomcat".
As Utsutsu monologues the sensation of being devoured, Yume is feeding off the flesh coming from Utsutsu's body, much to his agony. In their bloody act, Maria and a fellow reluctant subordinate monitors the sibling through the surveillance camera coming from Seto's cat eyes. Maria then recalls the time of Utsutsu's revival; while ordering her men to continue monitoring on Yume, Maria stumbles on a corpse-filled laboratory with a lone Utsutsu demanding the whereabouts of his sister, Yume. After Maria slashes Utsutsu's arm with a scalpel, Utsutsu discovers that he was also infected by a virus known as 'Pupa virus', granting him the ability of cellular regeneration. After explaining to Utsutsu the mechanics of the said virus, Maria receives an emergency regarding Yume. As Maria intends to capture Yume before her emergence, Maria, amused by Utsutsu's willingness to protect his sister, proposes the former to act as a living food source for his sister and shows him a drug that would temporarily suppress Yume from emerging. Utsustu agress without hesitation and rushes to Yume's aid as an eccentic Maria claims to have found her best 'guinea pig' yet.
After Yume's feasting of Utsutsu, the latter reassures Yume of being fine as he then wonders how to clean their bloodied sheets. Utsutsu then recalls his recent meeting with Maria regarding the drug. After explaining to the siblings of the drugs instructions and them being examined as an exchange, Utsutsu embraces Yume to reassure her that it's okay for him being eaten as it is worse than losing his sister as he recalls the harsh words coming from his father and pledges to protect his and Yume's everyday life.