The two-player aspect of the game came as a request from Shigeru Miyamoto, who thought multiplayer would fit Kirby even better than Mario due to the Kirby games' slower pace. Masahiro Sakurai, however, struggled a bit with implementing it due to multiplayer in other games awkwardly affecting things like the camera. Sakurai and his team eventually found workarounds to this dilemma in the form of the Space Jump mechanic, and what he described as a "Lead Player and Supporting Player" system.
Contributed by PirateGoofy