Kristina/Bree
Typically, people create alter egos to hide or escape from their lives or troubles. However, Kristina uses her Bree alter ego as a way to become a new person and to become more prominent.
Crank
At the beginning of the novel, Kristina views crank as a way to escape her problems and feel free from the burdensome shackles of her parents, but it ultimately enslaves her. She spends every waking moment of her life either seeking out or taking the drug. Her life becomes consumed by it; her addiction creates larger problems for her.
Kristina's pregnancy
Kristina falls pregnant after having a number of high-risk sexual encounters with the men around her. She believes that she can care for her child, which is ironic because she can't even take care of herself. Her addiction has caused her tremendous harm.
Kristina's mother
At the start of the novel, it is clear that Kristina and her mother are exceptionally close. She offers Kristina a sense of stability and love—two things that Kristina desperately needs in her life. However, as Kristina's needs grow, she ironically grows farther away from her mother and closer to drugs.
Kristina's love life
Kristina seeks love and affection with every action she takes. Still, her choices (particularly her drug addiction) often lead to toxic relationships that have neither love nor affection at their centers. That is especially true with her partners, Adam and Chase, neither of whom is a good match for her.