Rin is a human who shares her home with her twin sister, Len. Both sisters survived a tragic infancy accident that claimed their parents' lives. Following this event, Wooser rescued them, providing a new home and acting as a parental figure alongside Darth Wooser, a robot he created specifically to aid in raising and protecting the girls.

Rin possesses a calm, sensible, and collected personality. She consistently acts as the straight man, counterbalancing Wooser's erratic behavior and antics with her level-headed demeanor. This contrasts with her sister Len's more precocious nature. Despite Wooser's laziness, selfishness, and occasional inappropriate conduct—including his fixation on girls' school uniforms—Rin tolerates his presence and permits him to freeload. This arrangement stems from her view of Wooser and other household residents as family.

Raised under the care of Wooser and Darth Wooser after their rescue, Rin maintains an exceptionally close bond with Len. Together, they navigate daily life alongside Wooser and classmates like Yuu and Miho. Rin engages in various activities with her friends, such as forming an all-bass rock band, attending high school graduation, and enjoying beach trips. In one notable incident, she and Len transformed into magical girls to combat a giant Mecha-Wooser threatening the city.

Physically, Rin has brown hair, and specific measurements were revealed in an episode. She resides with Wooser, Len, and other characters, functioning as a stabilizing presence within the household dynamic.