Her parents are the one who force her to try Keijo. Usagi dislikes of how they force her to do that.
Usagi meets Mio at the entrance exam. Initially, Usagi had no interest with Keijo. However, after being motivated by Mio, Usagi is willing to participate in Keijo. Usagi adores Mio greatly, going as far to call Mio as "Goddess".
As Mio's admirer, Usagi feels jealous of how Nozomi gets closer to Mio. Despite this, when Nozomi states that she will invite Usagi to lunch with Mio, Usagi refuses, claiming that she just wants to admire her. While Nozomi considers that her personality is annoying. After being defeated by Nozomi, Usagi learns how to enjoy fighting in Keijo.
Both are fellow Outfighters. Rin knows that Usagi had no interest to participate in Keijo, as she is forced by her parents. However, Rin remarks that Nozomi is able to teach her how to enjoy fighting in Keijo.