Character Analysis
As Luna's trusted sister and the narrator of Luna, Regan is one of the most important characters in the book. Regan may be a typical teenage girl on the outside, but she's always working to protect her sibling's secret, and is therefore more closed off and cautious than most girls.
Secret Keeper
Regan's acted as Luna's secret keeper for as long as she can remember. Her first priority is always to protect Luna's big secret, even if it's at the expense of her own social life and happiness:
That was the first—and last—time Liam ever lost control. Why then? Why at my party, with my friends? That next week, Carmen began to act cold toward me. I didn't blame her; I don't blame her still. What kind of a person keeps secrets from her best friend? (5.184)
Regan's learned a pretty serious lesson early on: she can either choose to protect her sibling, or she can choose to have a social life. Because she loves Luna so much, she picks the obvious choice. She sacrifices her personal happiness and social possibilities in order to watch out for Luna, to make sure that she doesn't get hurt. But what Regan doesn't realize is that in doing so, she's hurting herself.
Lone Wolf
Because Regan is always confined to the role of her sibling's protector, she really doesn't have time to create her own life. Even though she's technically close to Luna, Regan still keeps to herself and tirelessly works to protect her sibling. She doesn't really tell Luna that much about her personal life; she doesn't even open up about boys or how she feels isolated at school.
And she's even worse with other people. When she meets Chris, Regan is immediately cautious—she doesn't want to get close to him because she doesn't want to deal with the repercussions of having to open up about her life to him. And on top of that, Chris is a cute boy, and Regan is way out of touch with normal flirtations.
So when Chris starts to make friends at school, it only confirms Regan's suspicion that everyone will pass her by and leave her alone:
A shroud of darkness descended over me. I don't know why I thought it'd be different. He'd be different. Someone as cool as him? All he had to do was cross the threshold of Horizon High to be instantly absorbed by Them. (8.39)
Even when Chris continues to pursue Regan, she doesn't trust it. She pushes him away emotionally because she doesn't know what else to do—she's always pushed people away. And her fears are somewhat reasonable—when she's with Chris, she doesn't provide the support for Luna that she feels like she should. For instance, she doesn't stand up for Luna because she's afraid of what Chris will think.
The good thing though, is that Chris surprises Regan and shows her that even if she's going to be a lone wolf in order to protect her sibling, he's going to keep pursuing her. He also shows her that he doesn't care about Luna—he doesn't judge her family at all.
Good thing Chris is persistent, because he manages to finally force Regan to open up and let another person into her pack.