Besides Final Fantasy, the Square-Enix franchise with perhaps the most rabid and devoted fanbase is that for Kingdom Hearts, a series which celebrates its 15th anniversary this year. The first title, which released on March 28, 2002, managed to strike a delicate balance between the worlds of Disney and Final Fantasy to begin weaving a story that hooked a huge following.

After a literal elevator pitch from a Square executive to a Disney employee – the two companies once shared a building in Japan – the series started development in 2000. The first game followed Sora, a young boy who obtains a weapon called the Keyblade and must fight against the invading creatures called the Heartless. Alongside Donald and Goofy, Sora travels to a number of different worlds (all of which are inspired by various Disney films) to prevent the Heartless from invading them. Eventually he must face off against Maleficent, who herself has been manipulated by a greater evil known as Ansem.

While a crossover between a hardcore RPG series like Final Fantasy and the many different franchises of Disney animation might seem odd, Kingdom Hearts managed to prove that it’s a formula that works. The first game eventually sold more than 5 million copies worldwide, and is one of the bestselling PlayStation 2 titles ever. That economic success was matched by critical praise, especially for the bright, lush visuals of the games.

The success of Kingdom Hearts spurred a franchise that, while it only contains two “main” games, consists of eight total entries thanks to the numerous spinoffs. What started as a PlayStation 2 exclusive has been seen on the Game Boy Advance, the Nintendo DS, and even mobile phones. And though fans have been patiently waiting for Kingdom Hearts III for several years now – with no actual release date in sight – their dedication to the franchise will likely show itself when that title does finally arrive.