In Turtles All the Way Down by John Green, the protagonist is Aza Holmes, and she must battle against a challenging antagonist, namely her mental illness, Obsessive Compulsive Disorder (OCD). There are several defining moments in the story as Aza tries to overcome her antagonist. Let's look at a few.

Aza's thoughts often drift to her fears, which are enhanced by her OCD. She continually makes her finger bleed, for instance, because she is terrified that she will get a particular type of bacteria. When Aza starts dating Davis, her OCD presents a new challenge. When the two kiss, Aza experiences severe anxiety, and she actually starts drinking hand sanitizer to try to cope with her fears. This is a defining moment indeed, and it seems like Aza's antagonist might win the battle. In the end, though, Aza gets the upper hand over her antagonist. While she still struggles and while she does not remain in her relationship with Davis, she comes to the realization that her illness does not have to control her. This is an excellent step in the right direction.

Now let's think about the powers of Aza and the OCD. Aza is fortunate to have the support of her mother, her doctor, and her friend Daisy as she copes with her illness, but there are still many people in the world who do not understand what it is like to struggle like Aza does. OCD is a powerful force that is not easily overcome, and there is still a stigma attached to it as well.