Usami is a member of the Shooting Star Subaru-Sama fan club (or the S4), but quit afterward and is also a member of the handcrafting club. She is shown to have considerable leg power which she uses in the form of kicks. She is shown to be a good cook, partly because she lives on her own and has to cook her own meals. She blackmailed Kinjirō, with the picture of him and Subaru on a mock date, to be her boyfriend up until the end of their school fair. Kinjirō accepted because of the condition that she will not spread the photo with Subaru and Kinjirō going out together.
She later becomes friends with Kinjirō and the others and is in love with Kinjirō. Her name is noted to sound similar to the Japanese word for "Rabbit" (ウサギ, Usagi), which becomes the source of Kinjirō's nickname for her; Usamin, her own nickname for him is "Stupid Chicken". She later allows Kinjirō to call her by her first name, Masamune.
As a gag, Usami is shown to be able to attract ghosts if not living together with them perfectly, such as ghosts appearing in her photos and randomly popping out in her apartment.