Square Enix's Kingdom Hearts series takes place in an unnamed outer space-like fictional universe with numerous self-contained worlds to explore over the course of play. Because the series is a collaboration between Square and Disney Interactive Studios, many of these worlds are based on animated Disney movies, though Kingdom Hearts II introduced some worlds based on live action Disney films. Sora's first journey takes him through each world to lock their keyholes and prevent the Heartless from destroying them. On his trip through Castle Oblivion, he revisits memory based versions of many of these worlds. In Kingdom Hearts II, Sora helps the residents of these worlds again in search of his friend Riku.
The Kingdom Hearts games have met with positive receptions and sales, as well as receiving several video game awards. One such award was "Best Art Style/Direction" in IGN's 2003 list of "Best Looking Games on PS2". As of December of 2006, the Kingdom Hearts series has shipped over 10 million copies worldwide, with 2.0 million copies in PAL regions, 3.0 million copies in Japan, and 5.6 million copies in North America. The graphics of the games have received numerous praise. IGN rated the graphics a 9/10 and stated that the "worlds look very much like their filmed counterparts." Japanese gaming site, Gpara.com also praised the look of the worlds. GameSpot referred to the worlds as "wonderfully rich familiar enivornments", and GamePro described the worlds as "spot-on with the original movies."