Michiru Saruwatari is a young Bushi princess of the Saruwatari Band, initially encountered facing imminent danger from an Oni until Musashi rescues her. She possesses average height, long dark hair typically tied loosely with distinctive horn-like locks, and striking golden eyes. Her initially cold demeanor masks profound shyness, gradually warming into approachability through interactions, particularly with Musashi.

She wields the specialized kitetsu blade "Lapis Lotus," featuring a dark blue blade and butterfly-shaped guard. This weapon manifests smaller blades in an umbrella-like formation, enabling defensive maneuvers and aerial suspension. Her combat style prioritizes utility and support, leveraging these properties for strategic advantages.

Her narrative prominence rises during the Uesugi Alliance's journey to Harima port to confront the Green Demon God Yamata no Orochi on Awaji Island. Traveling with a retainer, she crosses paths with Musashi, Kojiro, and Tsugumi in a forest. After being captured alongside Musashi by an Octopus Pot demon, they collaborate to escape, cementing her alliance with the group.

Michiru evolves from reserved observer to active participant in pivotal conflicts, joining the Uesugi campaign against Orochi. Her tactical awareness proves critical in perilous scenarios, such as strategizing survival during environmental hazards. She contributes significantly to missions like the offensive against the elite Oni faction Obsidian Eight. Throughout these engagements, her relationships and self-assurance deepen, establishing her as a recurring ally who influences both combat dynamics and character interactions across the series' arcs.