Sumire Mochiki, a former underground idol, left her career behind after enduring exploitation and disillusionment, pursuing a fresh start by enlisting in the military. Unable to meet the physical or psychological demands of becoming a Sleeper—operatives deployed into the perilous Asylum—she was relegated to the role of Sanity Anchor. Initially tasked with safeguarding Sleeper mental health during missions, the series’ waning focus on Asylum-induced insanity rendered her position largely symbolic.

She bears a prosthetic right leg, its origins tied to her past but left undefined. Her history as an idol, marred by exploitation and public scrutiny, fuels lingering self-consciousness and a reluctance to confront that era. This tension sporadically ignites friction within her team, particularly with the protagonist, though the specifics of their clashes remain unexplored.

Her design incorporates thigh-high boots, floral accents, and a twin ahoge hairstyle, echoing artistic sensibilities aligned with her passion for manga and anime. Despite her military obligations, traces of her performative past occasionally surface, hinting at unresolved struggles between her former identity and current duties.