Lena is the text’s second narrator and protagonist. Although not family to Magos and Joseph, Lena has been close to both for many years, and her narrative explores the complexities of chosen family and how grief affects everyone associated with a loss.

Lena’s character is fundamental to the development of the theme of Humanity Versus Monstrosity, as she firmly believes that monstrosity does not negate an individual’s right to love and acceptance. At first, Lena believes that Monstrilio is dangerous and should be destroyed. However, she quickly develops a fondness and a sense of “kinship” toward the creature. This affinity for Monstrilio stems from Lena’s own childhood, when her mother believed she was a demon incarnate and treated her like a “monster.” Now, as an adult, Lena’s sense of self-worth remains stunted, as she often feels unworthy, especially of loving human connection. For years, she has been in love with Magos, who doesn’t return Lena’s romantic interest.

In her professional life, Lena is a highly focused and successful surgeon. However, in her personal life, she struggles to form meaningful relationships. Instead, once a week, she pays sex workers to come to her home and bathe her—not seeking sexual gratification, but rather care and human connection of the kind she never experienced as a young child. Only in this transactional form does she believe herself deserving of intimacy. Lena’s relationship with Monstrilio begins to change how she sees herself. She sees Monstrilio’s monstrousness as the thing that makes him special. She loves him because of who he is, not in spite of it, and begins to consider the same possibility for herself.

Lena finally manages to forge a life apart from Magos and Joseph by moving to New York, telling herself she is “not a fucking speck” (163) and starting a life on her own. Although Lena and Magos reconnect, and she stays close to Joseph and M, Lena’s whole-hearted devotion to Magos never returns. She is able to maintain her self-worth and independence, even when Magos attempts to start a romantic relationship with her later in the story.

Joseph is the text’s third narrator. He is Santiago’s father and Magos’s husband.

When Santiago dies, Joseph’s reaction more easily conforms to what society often assumes is the “proper” way to grieve: His grief is easy to recognize as he sobs, loses weight, and falls into a depression that leaves him bedridden. He “withers” in a way that Magos resents, with Joseph in turn being initially unable to recognize Magos’s intense, silent suffering. Joseph, for his part, is horrified by how Magos mutilates their son’s body and takes her lack of visible grief as a sign that she “didn’t care Santiago died” (76). These differing reactions to their son’s death strain their relationship and ultimately drive them apart.

For a time, Monstrilio brings Magos and Joseph back together. Joseph quickly bonds with the creature, finding his monster form so different from his son and therefore “easier to love” (241). Unlike Magos, Joseph never believes that Monstrilio is Santiago. However, he also doesn’t celebrate Monstrilio’s monstrosity quite as thoroughly as Lena does. As Monstrilio grows, Joseph encourages “his steps into humanhood” (199), urging him to quell his appetite and to conform to social norms. Joseph believes that Monstrilio “has a right to be human” (194). However, he also recognizes at other moments that, by encouraging Monstrilio to become human, he might be forcing Monstrilio to be someone he isn’t. He wants to celebrate Monstrilio’s true self, but recognizes that he isn’t “strong enough to take on whatever consequences came from setting him free” (197).

Joseph’s narration takes place seven years after Santiago’s death. He has moved back to New York and is engaged to Peter, slowly “shedding […] Magos, Santiago, and M” (173). Consciously, Joseph longs to let go of his pain and start fresh. He has grieved his lost son and is ready to release him. However, his intense fear of losing Monstrilio suggests that Joseph isn’t as ready to move on as he believes. Joseph’s fierce and immediate defense of M when his monstrous tendencies get the best of him, as well as his insistence on trying to make M more human and hide the truth of his identity from Peter, suggest that Joseph is more attached to his painful past than he can acknowledge. At the end of the novel, he and Magos finally come to terms with their grief together, willingly releasing M into the wild.

M is the fourth and final narrator of the text. Staring out as a piece of the deceased Santiago’s lung, M develops first into Monstrilio, a frisbee-shaped hairy, carnivorous monster with a wide mouth of fangs and a single appendage like a tail ending in a clawed paw. As long as he is kept well-fed, Monstrilio is relatively harmless: He is playful and joyful, swinging happily from his arm-tail on the jungle gym that Joseph builds for him. Monstrilio is charming, quickly winning the affection of those close to him, especially Lena and Joseph.

However, each person close to Monstrilio loves him for a different reason that may or may not have anything to do with Monstrilio himself. Magos sees Monstrilio as her son reborn; Joseph knows that Monstrilio isn’t Santiago, but sees him as a kind of second son to nurture, raise, and distract himself from his loss; Lena sees the creature as proof that the things she considers monstrous about herself do not negate her right to love and connection. In this way, Monstrilio becomes a mirror for those around him, but at the cost of his own sense of self.

When Magos decides that Monstrilio’s arm-tail must be amputated so he can “evolve,” Lena and Joseph are against the idea, arguing that Monstrilio is “supposed to be” wild and that he should be loved for who he is (149). After the operation, Monstrilio falls into a deep depression, leaving Lena and Joseph wracked with guilt. Eventually, he does develop into a human-shaped creature, whom Magos calls “Santiago,” and others refer to as “M.” However, the narrative from M’s perspective reveals a deeply confused and conflicted being. He is a conglomeration of Santiago, Monstrilio, and the newly developed M, sometimes referring to himself with the collective pronoun “we.” He has clear memories belonging to Santiago and to Monstrilio, leaving M somewhere in the middle, very aware that his humanity is a collective act put on by him, Magos, and Joseph.

Initially just a mouth with no other features, M continues to be defined by his appetite even as his shape becomes more human. He longs to consume live flesh, preferably human, a tendency that Magos and Joseph urge him to contain, assuming he will eventually grow out of his hunger. However, M is “hungry all the time” (273): Becoming more human doesn’t lessen his appetite, it just makes him feel like his hunger is something to be ashamed of. As he grows and begins exploring his sexuality, M asks his lovers for permission to bite them. When one young man who turns out to be a part of a cult gives him permission to eat him, M does, refusing to stop even when the man changes his mind and begs him to desist. Faced with the horrified reactions of his family, M cannot see how he did anything wrong, realizing he cannot be human after all.

By the end of the text, M starts to let go of his attempt at being human and begins accepting his own monstrosity. His arm-tail starts to grow back, and hairs from the room where he ate the man are identified as belonging to a “wild animal.” When Joseph starts offering ideas to control M’s hunger, he stops him for the first time, telling his father, “I know what I want to eat” (312). While back in the house where Santiago died for the occasion of Joseph and Peter’s wedding, M sheds his human charade for good, saying goodbye to his family and returning to the wild. Despite his tireless efforts and those of his family, his true nature could not be fully repressed or overcome.

Uncle Luke is Joseph’s closest living relative. He is an elderly man who doesn’t speak, but communicates solely through grunts and writing. He is also intimately familiar with loss and grief. When Joseph was a child, his mother died, and Uncle Luke “absorbed all the grief and accumulated it inside his body” to keep it away from Joseph, making his own body “gnarled and bent at odd angles” (74). Uncle Luke’s life has been physically transformed by grief, putting him in a unique position to understand Joseph and Magos’s loss.

Out of all the characters, Uncle Luke is the most accepting of M. In fact, he “celebrates” M, calling him “incredible” and reminding Joseph that “M is M” (197) when he expresses any desire to control or change him. Due to his “gnarled” body, muteness, and isolation, Uncle Luke understands what it is like to be different and to have one’s life shaped by forces outside of one’s control. In M’s wildness, Uncle Luke sustains “a belief in a pure freedom” (178). He is the only character who doesn’t place constraints on M and encourages him to be himself.