Michiru Saruwatari is a young woman from the Saruwatari Band, a group of bushi operating under the Uesugi Alliance, where she holds the status of a princess. She has a distinct appearance with long, dark hair tied loosely and featuring horn-like locks, as well as large golden eyes. Initially, she comes across as cold and distant, but this demeanor is actually the result of a severe case of shyness. Michiru herself admits to being a recluse and struggles to join conversations involving three or more people, which makes her seem reserved or even unapproachable. Despite this social difficulty, she possesses a gentle and caring nature that becomes more apparent as she grows more comfortable around others.

Her motivation is largely tied to her duty to her family and her band. She is sent by her father to take part in a decisive battle, and it is during her journey to the port of Harima that she encounters Musashi and his companions. Michiru is rescued by Musashi when she is about to be devoured by an oni, and this event establishes a strong bond between them. Her relationship with Musashi is particularly significant; she eventually opens up to him, and her subtle charm is noted as being capable of stirring his heart. Over the course of the story, Michiru develops from a shy and withdrawn figure into a more confident and reliable member of the group, though she retains her underlying timidity.

As a bushi, Michiru is skilled with a blade. She demonstrates the ability to use her sword creatively, such as turning it into a makeshift flying umbrella to save herself and Musashi from a fall. Her role in the narrative is primarily supportive, providing both combat assistance and an emotional anchor for the main characters, especially Musashi. Her character arc involves overcoming her social fears and learning to trust her companions, which allows her to fully participate in the group's efforts against the oni.