In the nation where steam breathes—Jōkipon. Seventeen-year-old rookie courier Tenshi is assigned his very first solo delivery. His mission is simple: deliver a sealed message cylinder. "Protect the seal more than the contents." Carrying a Kinetic Core powered by steam and momentum, Tenshi races from rooftop to rooftop. Floating spinning tops played by children. Steam Samurai in training. Ancient Steam Torii. And the enormous gate that seals off the edge of the world. This is not the tale of a legendary hero. It is the story of one rookie courier's first journey through the city, the people he meets, and the world he discovers. Come run through Jōkipon together with him.