Moburi-san acts as an older sister figure to Mattsu and Yamma, two boys living in Matsuyama. Her name comes from the Matsuyama dialect verb "moburu," meaning "to mix and combine," reflecting her narrative role of bringing elements together.

Aged 17, she is a high school student passionately interested in history, a perspective that informs her during the adventure. She frequently rides her bicycle, indicating an active lifestyle.

Her involvement in the central plot begins when two men arrive seeking the "seven hidden gems." This event entangles her fate with Mattsu and Yamma's ongoing search for "the seven wonders of Matsuyama." She becomes caught in the unfolding mystery surrounding the gems and a flying castle. As the situation escalates, the group faces challenges demanding decisions that will impact their city's future.