Tsutomu Saki serves as a pacifist pilot aboard a Cosmo Ecology space freighter in 2061. This organization operates under an international treaty dedicated to combating space pollution, specifically processing hazardous waste on Jupiter to prevent illegal dumping of radioactive materials into the sun, which dangerously increases solar flare activity threatening Earth. Saki transports this waste, though he initially struggles with basic piloting tasks, sometimes causing collateral damage during shipments. Despite this apparent operational clumsiness, he possesses deep technical knowledge of spacecraft systems, frequently explaining their functions in detailed techno-babble.

Saki's defining trait is an absolute commitment to nonviolence. During a mission investigating satellite wreckage, he insists on sparing the life of outlaw soldier Jimmy Dean, even when fellow pilot Robert Ryan faces imminent danger. Saki argues against lethal force, attempting dialogue to de-escalate the conflict. His pacifism drives him to intervene directly when Jimmy Dean prepares to self-destruct his ship; Saki pilots into the combat zone to negotiate a surrender, emphasizing trust in humanity's capacity for change. He consistently maintains that killing is never justifiable, including in self-defense.

The narrative traces Saki's evolution from a marginalized crew member, criticized for his pacifism and perceived ineptitude, to an active proponent of his ideals. He demonstrates resolve by maneuvering his ship under fire to assist Ryan. His technical expertise proves vital in non-lethally disabling Jimmy Dean's vessel, directly aligning with his ethical stance. Saki's personal appeal for compassion ultimately persuades Jimmy Dean to abandon his self-destructive plan, positioning Saki as a catalyst for reconciliation. His motivations stem intrinsically from principles of environmental preservation and anti-violence.