The core of Mashiro’s character arc lies in her contrast with Sorata Kanda. Sorata is an "ordinary" person striving to be extraordinary, constantly battered by rejection and failure. Mashiro, conversely, is naturally extraordinary, succeeding effortlessly in fields she applies herself to (first oil painting, then manga).
Throughout the series, Mashiro’s presence acts as a catalyst for growth for everyone in Sakurasou.