Natsume

Natsume is a young woman who is an itinerant martial artist along with her younger sister, Kurumi. For years the two wandered Japan in search of their long-lost father, Soun Tendo. They briefly usurped Akane Tendo and Ranma Saotome’s claim to inherit the Tendo Dojo and carry on Anything Goes Martial Arts after challenging and defeating them, but conceded their claim following a rematch.
Both sisters are the only characters to appear in the OVAs who did not originally appear in the manga.

(Source: Ranma Wikia)