Prior to the destruction of Robledo, Harold "Harry" Balter is Joanne Garfield's boyfriend, despite the fact that they're—oops—cousins (4.28). Once Lauren's hometown is destroyed, he pairs up romantically with Zahra (17.32). Harry's a white guy (4.28), he doesn't get along with his father (5.67), and he thinks that Olivar is a big debt trap (12.15-16). In a nutshell, Harry's a bit rebellious, and for that reason, he makes a good teammate for Lauren.
Lauren and Harry don't interact much prior to the destruction of Robledo, but once their hometown is destroyed, the two have to work together. Harry rescues Zahra from rape (14.104) during the destruction, and that rescue kind of forms the basis of their kinda sorta relationship. At first, they join with Lauren simply because they know one another from the town and need allies. Once Robledo is out of the picture, Harry wants to find a job in the north somewhere (15.24), so much so that even when they all get to Bankole's land, he resists the idea of settling there a at first since there's no paid work available (25.46-47).
As Lauren and company migrate north, Harry's the one who most questions Lauren's changing attitudes about whether to welcome strangers or ward them off. Early in their journey, Lauren turns away some people seeking food and help—including an old guy Harry wanted to let sit with them (16.11)—and Harry says to her: "What, then? [...] Everyone's guilty until proven innocent? Guilty of what? And how do they prove themselves to you?" (16.15).
Yeah, Harry's not having it.
But a few chapters later, Lauren starts helping Emery and Tori and others, and that leads Harry to tell her: "I say you're going soft" (23.62), because Lauren "would have raised hell if we'd tried to take in a beggar woman and her child a few weeks ago" (23.62). Seems Harry is happier with the friendlier Lauren.
Maybe some of the credit for Lauren's change should go to Harry, since with his constant commenting, he's one of the main forces responsible for prompting her to think over how they should treat others.
Harry doesn't seem to go in much for Earthseed, despite listening to Lauren talk about it during their journey. At one point, Lauren notes that he "refused to take the discussion seriously" (18.57). At other times, he says "Amen" as a joke (18.53) or mischievously identifies their group as "Earthseed" (19.105) to strangers. It seems that maybe he's flirting with the idea of finding faith in her religion—or maybe he's just too focused on trying to get to a place where he can make money to survive.