Corrie is Ellie's BFF and her partner in crime for setting up the camping trip the teens go on before the invasion happens. At the start, Corrie's right by Ellie's side, but after the camping trip she drifts off with Kevin. Corrie's still around, she's just not kicking it with Ellie non-stop any longer. Still, though we don't see her too much, Corrie is an important person in Ellie's life and as the book ends, Ellie's anxiously waiting to hear whether Corrie's made it to the hospital for much-needed medical treatment. Fingers crossed.
Ellie might daydream that Fi has it all—she's pretty, wealthy, and has a body Ellie thinks is perfect—but Fi's perceived gifts aren't nearly as useful as Ellie's experience and skill while the world as the teens know it is coming to an end. In fact, being a stereotypical popular girl does little more for Fi than earn her Homer's affection.
To be fair, Fi is as sweet as can be and generally pretty willing to help. By the end, she even helps build fencing to contain the gang's chickens. She is important in the story because she becomes Ellie's mirror, offering Ellie a point of reference to compare both herself (particularly her looks and her femininity) and her feelings for Lee too (particularly in relation to Fi's feelings for Homer). In other words, much as Ellie might feel like Fi has it made in the shade, Fi's really just a tool in this book to help Ellie—and by extension, readers—better understand Ellie's character.
This chick is tough, a natural leader and quite smart. There is no love interest for Robyn, but she does think often about God and the bible. She encourages Ellie to turn to prayer, which does help Ellie feel better sometimes. We don't see or hear from Robyn much, but she's always around, and she's always helping.
This is Corrie's man, and even though he is a little finicky, immature, and wishy-washy, she still loves him. Why? He cares about her and is a good friend in the ways she needs him to be. For example, when the kids check out Corrie's house and find it empty, Corrie gets totally overwhelmed. Kevin goes right to her and holds her: "They stood there for quite a few minutes. I liked Kevin a lot for that" (7.12). We do, too, Ellie; we do, too.
Tenderness for Robyn aside, Kevin is a bit aggressive and argumentative at times, though he's also pretty scared and passive at others. He is not a main character or a major player—well, except in Corrie's heart. Aw.
Chris hangs out at the periphery of the Hell gang's exploits. Not only does he join in late in the game—they come across him while stealing his family's car—but he also isn't a major player in the narrative. He is moody and smart, but doesn't contribute much of his brains to the community. Mostly he just wants to smoke and drink alcohol.