Jun is a shy young boy whose profound empathy for the natural world starkly contrasts humanity's widespread pollution and environmental neglect. He expresses his appreciation through reading poetry and nurturing flowers, behaviors that provoke bullying from peers and familial tension over his educational choices and perceived effeminate qualities.

Identified by an extraterrestrial intelligence as one of the rare humans retaining genuine empathy, Jun is transported alongside Remi and Chobi to the Mesozoic era. Their mission is to learn about ecological balance, extinction, and the consequences of human actions. Throughout this prehistoric journey, Jun primarily observes, witnessing key events like dinosaur behaviors, the volcanic-induced climate catastrophe ending the Cretaceous, and the subsequent rise of mammals. His sensitive nature shapes his reactions to these events, though he takes no significant proactive steps against dangers like the Tyrannosaurus.

Jun's development remains subtle. The alien's lessons and his visceral exposure to prehistoric life, death, and mass extinction powerfully reinforce his pre-existing environmental consciousness, underscoring the urgency of stewardship. His core traits—passivity, compassion for nature, and quiet resilience—persist unchanged throughout the narrative.