Shunki Sa

The granddaughter of Enjun (Sa-Taihō), her father and mother were murdered nine years ago by her cousin, Sakujun Sa, though that fact is unknown to her. Her ability to speak was sealed by her grandmother, Eiki, when she was a child, and so she communicates primarily through writing. Because she is of the main Sa line of descent through Enjun, she is a threat to Chūshō and other branch family members during their power struggle. For her own protection, she is hidden away and watched over by Shōrin and Yōshun, under orders from Ensei Ro. Later, she uses her strange power to rescue Kokujun together with Shurei.

When Kokujun accepts the burden of leading the Sa clan, she vows to be always by his side. (Source: Wiki)