The second protagonist, Keith is a high school student navigating the uncertainty and isolation of adolescence. His journey is marked by his changing attitudes towards relationships, intimacy, and his place within social groups.

A supporting character seen through Keith's perspective, Eliza is a resident at a house associated with Keith's friends. Her life and experiences, particularly in the realm of relationships, form a key part of her interactions with Keith.

Rob is Chris's romantic interest who inadvertently passes the Bug to her. His second mouth, a symptom of the Bug, provides insight into his subconscious thoughts and complicates his interactions with others.

A supporting character who becomes an antagonist, Dave is a high school student marked by his experiences of bullying and social rejection. His feelings for Chris and actions at the camp are central to the unfolding of key events.