Tetsudō Hisakawa, universally called "Poppo," stands as a core member of the childhood friend group known as the Super Peace Busters. His youthful appearance featured a shaved head and casual attire like a blue hoodie and track pants. He idolized the group's leader, Jinta "Jintan" Yadomi, repeatedly calling him "amazing" or "cool," and cherished his inclusion in the group, feeling socially awkward himself.

After their friend Meiko "Menma" Honma died accidentally in childhood, the group fractured. Presently, Tetsudō abandons school for a nomadic existence, financing his travels through transient jobs like construction. He intermittently lives in the group's old secret base. Externally, he projects a worldly, cheerful, and mellow persona, often mediating conflicts. He instantly believes Jinta's assertion of seeing Menma's ghost and dedicates himself to fulfilling her final wish for peace.

Beneath his relaxed facade, Tetsudō nurses crushing guilt over Menma's death. He preserves flowers from her accident site in a pouch necklace—a perpetual token of his unresolved trauma. During emotional clashes, his calm shatters, exposing raw anguish over his perceived failure to save her. This pain erupts in a cathartic group confession where he and others voice their enduring grief and self-blame.

Having helped Menma move on by achieving her wish, Tetsudō confronts his past. He pursues his high school diploma while maintaining part-time work. Years later, he co-founds a company with Jinta. He becomes the sole Super Peace Buster to marry and raise children, signifying profound personal evolution beyond his earlier rootless life.