Japan's cargo ship did not dock with the space station. It stopped nearby and waited to be caught.

A spacecraft can dock — fly itself into a mating ring under its own guidance, with all the risk that carries near a crewed station — or it can be berthed: stop at a safe distance, hold position precisely, and let the station's robotic arm capture it and move it to a port. Berthing puts the final, most dangerous metres under the control of the crew and the arm rather than the visiting vehicle's autopilot, and it allows a much larger hatch, which is what lets big payloads through.

The vehicle was designed to deliver up to six tons of supplies — food, clothing, experiment equipment — to a station orbiting around 400 kilometres up, and to depart loaded with waste. Its distinguishing capability was bulk: it could carry multiple large pieces of experimental equipment, and station batteries, on a single flight. That is only possible through a berthing port, and berthing is only possible if the vehicle can hold still and be caught.

Japan also had to build the conversation that makes the approach safe: the Kibo module carries a Proximity Communication System, developed for KOUNOTORI, letting the resupply vehicle and the station talk directly to each other rather than through the ground. The approach method it proved — grapple with the arm, then berth — became the standard for reaching the ISS, adopted by privately developed American supply craft including Cygnus and Dragon.