X was originally pitched under the name Eclipse and was developed under the title Lunar Chase. The single-letter rename came at the request of Nintendo president Hiroshi Yamauchi, who contacted director Yoshio Sakamoto early in the morning after playing the game.

The Lunar Chase name was retained for a planned English localization of the game, which was ultimately scrapped due to fears from Nintendo of America that international players would find the game's presentation and design too complex for a handheld title. Creator and programmer Dylan Cuthbert additionally blamed the cancellation on a presumed lack of interest from retailers in the United States. A prototype of the English version would eventually surface in 2020 as part of the Gigaleak, a massive leak of internal server data from Nintendo. The Eclipse pitch, meanwhile, was released to the public by the Video Game History foundation three years later.