Jake might be the typical annoying little brother that tends to show up in young adult novels, but in Kristina's case, he's a lot more than that. The child of Kristina's mom and her second husband, Scott, Jake's arrival disrupted what remained of Kristina's old life by changing the dynamic between her, Leigh, and their mother. Kristina describes him in the book's opening as "spoiled and shameless in his thievery of my niche" (Alone.2), reducing the former youngest daughter to middle-child status.
A "ministud athlete" (My Luck Ran Out.2), Jake's zeroed in on sports as well as annoying his older sisters. He's also a little too inquisitive, which is probably a bad thing given Kristina's extremely adult situation. Check out the part where Kristina's parents show up to get her out of juvenile hall. "Jake was enthralled by the whole idea of my temporary incarceration and the reasons behind it," Kristina tells us. "He wouldn't shut up about it, just kept asking inane questions" (Cause and Effect.5). Uh-oh… hope he doesn't think she's cool for this jail stint.
Could Kristina's story function without Jake? In all honesty, it probably could. But with her parents' dysfunctional first marriage at the heart of Kristina's brokenness, a child between her mom and Scott adds significant stress to her already distant home situation. He might be little, but because of this, Jake matters.