When our story begins, Rafe only has one living sibling—nine-year-old Georgia. Georgia's like most little sisters in the history of humankind, because her big brother thinks she's a "super-nosy, super-obnoxious, super-brat" (1.11).
Little sisters—you can't live with them, you can't ship them off to a desert island until they move away from home.
Georgia is always kind of lurking around in the background annoying Rafe. She's also not the greatest at keeping secrets. She's the one who tells Mom that Rafe stripped down to his underwear on Halloween. Rafe also strongly suspects she might spill the beans about his secret Zoom-smuggling operation. She's kind of like the anti-Rafe as far as honesty goes, though she does manage to keep the disappearing soda cans to herself.
But for all his complaining about annoying little sisters, it's clear that deep down, Rafe totally loves and cares about Georgia. He hates when Bear yells at Georgia so much that he will actually defend her even if it means getting yelled at himself:
I hated when he yelled at her like that, even more than when he yelled at me. She's just a little kid and he's—well, he's kind of like a little kid too, but the biggest, meanest little kid you ever saw.
"Pick on someone your own size!" I yelled down the hall. (17.8-9)
Later books in the middle school series are actually told from Georgia's point of view. Specifically, she has to deal with people who have preconceived notions about her because of her rule-breaking big brother Rafe. In many ways, Georgia's kind of the opposite of Rafe—but she winds up finding out that middle school can be tough for all different types of kids.