Corpus Hamel, or the false Hamel, was a Great Existence responsible for the descent of BR-001. It envied Hamel for the adoration she received from everyone in the Carnival, and impersonated her in order to draw Corruptors close. The Corpus's instincts were deeply influenced by the desires for safety and acceptance of the carnival-goers whose Mania provided it with the power to call down the Black Ring. This is reflected in the final acts of the Hamel Corpus, as it felt unfulfilled with eating the ordinary Corruptors in the Carnival and believed that it could only be satisfied by devouring the Chief and gaining the "companionship" of the other Inheritances inside them.
Because it mimicked Hamel, the Corpus possessed a version of her Blissful Illusion ability that allowed it to access memories and create illusions of people's mental images to exploit their emotions. Unlike the real Hamel, the Corpus was never able to learn to care for anybody but itself. Its full awakening was prevented for years by Hamel, who created an illusory world that subdued the emotions of the Corpus and Corruptors in the Black Ring. During this time, Parma gradually funneled contamination into the Carnival, which would eventually have upset the balance of power in the Ring and allowed the Corpus to break free. Before this could happen, it was defeated by the Chief and was consumed by them.
Role
Endless Carnival
Hamel immediately detects the arrival of the MBCC team when they approach BR-001. As they watch, it devours the essence of the Corruptors who were drawn to her. Hecate attacks her, and Hamel is surprised to find that they don't love her like the Corruptors do, but is unharmed by the assault and is revealed to be an illusion. Upset, it disappears back into the Black Ring.
Later, while the Chief is struggling to remain in the Carnival, a fragment of the Corpus in the form of a doll offers to lead them to Hamel. It brings them to a Ferris wheel where they encounter a man in a black raincoat, who listens to the doll's wish to dance for everyone. The man announces that he will grant its wish, then incinerates himself and surrounding Corruptors with black fire. The doll consumes the fire and grows into another illusory Hamel, who attacks the Chief and Hecate with similar fiery powers. However, it is stopped by the appearance of the Misery Puppet, who tells it that it shouldn't contaminate the park or harm the dancer, and banishes it with its white smoke.
The dark Hamel appears again at real Hamel's lake, leading a host of Corruptors to stop the real Hamel's dance. It is driven away when Hella and Hecate break free from their prisons, but rejoices anyway when the Chief convinces Hamel to end the illusory world. With the real Hamel no longer keeping her subdued, the Corpus begins to feed freely on the Corruptors in the park, imitating Hamel to draw them to it before devouring their Mania contamination. However its real target is the Chief, and it devours them. It attempts to exploit the Chief's fears and regrets through its illusions, but they are unfazed by its tricks and use the Shackles to drag it back to reality. Before they can destroy it though, Parma appears and rescues it. The Corpus is distraught that even now someone still does not love it like Hamel, and Parma soothes its worries. The Corpus realizes that the Chief is the same kind of existence as it, and goes to wait for them to reach its main Corpseborne body.
Atop the Carnival's Ferris wheel, the Corpus uses illusions to grants the wishes of the Corruptors who come to it looking for Hamel, but it struggles to understand their desires and provides unfulfilling solutions to their needs. She eats these Corruptors, but is unsatisfied by this fare, and decides that what she requires is the Chief -- likely because they now contain several Corpuses, which frequently seek to absorb each other. When the Chief approaches the Ferris wheel, it consumes them again and almost devours their essence, but the Chief is freed when they hear the voice of Hamel and are rescued by Hella and Hecate. The Chief then plucks out the Corpus's core, and it is absorbed into them.
Following the false Hamel's defeat at the hands of the Chief, Parma mentions that he couldn't have expected much of a wild Corpus that had gone without proper nurturing.