LitCharts assigns a color and icon to each theme in The 5th Wave, which you can use to track the themes throughout the work.
Trust and Belief
Survival and Perseverance
Warfare and Dehumanization
Family
Summary
Analysis
When Cassie opens her eyes, she cries about having to leave that pleasant feeling. Evan says he never wanted to exterminate humans—he always argued for trying to coexist with them. Evan has been in a human body for a while but didn’t feel fully human until he saw himself in Cassie’s eyes. He assure Cassie he’ll be on her side.
Cassie’s tears after the bliss of seeing Evan’s true form show how happiness and sadness are related emotions. Cassie’s sudden swings in emotions reflect both the volatile time she lives in as well as the difficulties of growing up more generally.