Kingdom Hearts: 358/2 Days (pronounced Kingdom Hearts Three-Five-Eight Days over Two) follows the story of Roxas during his time in Organization XIII. The game mainly consists of Roxas doing missions for the Organization by going to various worlds (such as Twilight Town, The Beast's Castle, Agrabah, etc.) to collect hearts by defeating the Heartless, gather intel, and collect Organization Emblems. The story will explain Roxas' origins from the moment of his creation at the end of Kingdom Hearts to the point when he is placed in the virtual Twilight Town before Kingdom Hearts II.
All missions are started in "The Grey Area", one of the Organization's Headquarters, in which Roxas can equip different "panels" to boost his level, gain new abilities and magic spells, or bring items to use on his missions. Munny (currency in Kingdom Hearts games) and Heart Points can be spent at the Moogle Shop to acquire more panels to equip in the panel grid.
All completed missions can be played again by using the holo-mission option in the menu. Some missions also unlock some challenge modes (in which you must complete the same mission under certain conditions such as jumping as few as possible, collecting more hearts or munny, or doing it really fast) and some can also be played in mission mode. The mission mode is accessed from the start menu and allows multiple player to collaborate and compete with each other. They can use any of the Organization's members and the player who accumulates the most points wins Crown Emblems.