Hana is your typical Young Adult BFF: gorgeous, glamorous, coordinated, popular. Basically, she's everything Lena, our heroine, is not. Hana has the power to make boys look at her, the power to turn the world on with her smile. She's the Mary Tyler Moore to Lena's Rhoda… if Rhoda were a boring hermit with an irrational fear of everything.
We see them fight a lot in Delirium. Mainly they clash because Hana is doing everything that Lena wishes she could do, but is too afraid to. Over the course of the book, Lena becomes increasingly irrational, and seems determined to lash out at Hana in the most vindictive and petty ways possible. Perhaps instead of BFFs they're BFFNs: Best Friends for Now.
Frankly, we're not sure why they're even friends. Or why Hana doesn't seem to have any other friends. Even though she occasionally hangs out with other girls, we're told that Hana "never really got close close with anyone besides [Lena]" (8.3).
The two met because of a school project, and Lena likes Hana because she's nice to her even though she's always crying about her terrible (but actually very normal for this dystopia) life. And how does Lena repay this niceness? By being a big jerk to Hana.
Lena is constantly determined to find flaws in Hana, and feels jealous when she can't spot any. Lena takes great pride in the fact that she runs faster than Hana, because she feels it's the only thing she can do better than Hana the Perfect. And when Lena meets Alex, she ends up running right out of Hana's life.
And you know the first rule of being a true BFF, don't you, ladies? Never ditch your longtime friend for your new boyfriend, are we right?
Lena's aunt seems to disapprove of her friendship with Hana. (Well, she disapproves of everything, to be fair.) She tells Lena, "you came from different starts and you'll come to different ends" (12.21). "Different starts" means that Lena is poor and Hana is not. Hana has a nice mansion with electric appliances. In the future, every girl dreams of having a washer and dryer, we guess. Retro sexism FTW?
Anyway, Aunt Carol's prediction comes true. You're shocked, we know. But these two characters do come to different ends. Lena decides to run away into the Wilds, and Hana decides to stay. "Turns out you're braver than I am" (24.63), Hana tells Lena.
Hana pretty much exists to show that a pretty girl—who seems to hold all the power in life, simply by virtue of being attractive—can still be less awesome than an average-looking girl. She ends up conceding that she owes Lena her life, that Lena is braver than she is, and that she'll put Lena first. This is pretty much the opposite of what we think of as an equitable relationship.