Setsu grows up in a late nineteenth-century rural Japanese village alongside Tatsunosuke, forming a foundational childhood bond. She becomes his wife after he establishes himself as a successful lamp salesman and service provider, their marriage coinciding with his business expansion during sweeping technological shifts toward Western imports like oil lamps.

As Tatsunosuke's spouse, Setsu actively participates in domestic life and supports his trade. Together they raise two children, her daily routine intertwined with the lamp business, reflecting its role in community life.

Setsu's view of technological change contrasts with Tatsunosuke's resistance. When electrical lighting emerges as a superior alternative, she and their children exhibit fascination, embracing its convenience and modernity during village meetings where residents vote to adopt electrical infrastructure, highlighting generational divergence.

Setsu witnesses Tatsunosuke's crisis of identity and livelihood, driven by obsolescence fears. She observes his emotional deterioration and desperation, culminating in an abandoned arson attempt to sabotage the village's modernization when he recognizes his loss of self. She is present for his tearful decision to formally terminate the lamp business, symbolizing surrender to irreversible change, underscoring the personal impact on their family.

Setsu's narrative arc demonstrates adaptation to societal transformation. Her transition from reliance on lamp-based lighting to accepting electricity mirrors broader cultural shifts, positioning her as representative of communities navigating progress's human costs. Her role centers on familial stability amidst upheaval, contrasting Tatsunosuke's struggle while embodying pragmatic resilience.