Sanae Shiratori, orphaned by the Zaal Empire's invasion of Earth, endured the searing trauma of watching her parents perish in a burning building during the assault. Civilians physically prevented her from attempting a doomed rescue, an event that left enduring psychological scars. In the aftermath, she formed bonds with fellow orphans, including Ochame, whom she invited to cohabitate after recognizing their shared survival.

Driven by compassion, Sanae aided the injured Danji Hiiragi, sheltering him in the group’s hideout—a decision that solidified her place within the survivor collective. She embraced a maternal role, nurturing younger members like Ochame, Jiro, and Manabu. Though she initially clashed with Kento Tate over his food thefts, she reluctantly adapted to morally ambiguous survival tactics as post-invasion hardships escalated.

A pivotal moment arose when she resisted a stranger’s offer to adopt Ochame, later exposed as Zaal General Neshia’s deception. This confrontation highlighted her fierce protectiveness and unwavering loyalty to the group. Her past received detailed exploration in an episode chronicling her loss, Danji’s rescue, and her early connections with Kento and Ochame.

Operating within an ensemble framework, Sanae’s interactions underscored wartime themes of communal endurance and improvised familial bonds. Her guardianship of Ochame and evolving dynamic with Kento cemented her as the group’s emotional anchor. No official media appearances beyond the main series are documented.