Moxie features a transgender character, Kaitlynn, who faces exclusion from the girls' soccer team. The film's narrative strongly supports Kaitlynn, portraying the discrimination she experiences as an injustice. The protagonist and her allies actively challenge transphobic policies, advocating for inclusion and affirming Kaitlynn's identity and right to participate. The overall portrayal is supportive and validating of LGBTQ+ identity.

The film features characters whose race differs from their established portrayals in the source novel. Claudia, generally depicted as white in the book, is portrayed by an Asian-American actress. Seth Acosta, implied to be Hispanic in the novel, is portrayed by an Asian-American actor.

The film portrays a single-parent household where the mother's independent lifestyle and new relationship are normalized. It champions the protagonist's journey to challenge traditional gender norms and societal expectations, emphasizing individual empowerment and the strength of chosen communities.