Kingdom Hearts (キングダム ハーツ, Kingudamu Hātsu) is a series of action role playing games developed and published by Square Enix. It is a collaboration between Square Enix and Disney Interactive Studios, and is under the direction of Tetsuya Nomura, a longtime Square Enix character designer. Kingdom Hearts is a crossover of various Disney settings based in a universe made specifically for the series. The series features an all-star voice cast, which includes many of the Disney characters' official voice actors and well-known actors such as Haley Joel Osment, David Gallagher, Jesse McCartney and Hayden Panettiere. Characters from Square Enix's Final Fantasy series make appearances and interact with the player and the Disney characters. The series centers around the main character Sora's search for his friends and his encounters with Disney and Final Fantasy characters on their worlds.
The three main games in the Kingdom Hearts series focus on the adventures of Sora and his friends, Kairi and Riku. The first game shows how Sora is separated from his friends when their world, Destiny Islands, is invaded by creatures known as the Heartless. During the invasion, Sora obtains a weapon to be able to fight off the Heartless, known as the Keyblade. Soon after finding himself in Traverse Town, Sora meets Donald Duck and Goofy, two emissaries from Disney Castle searching for the "key" per instructions from King Mickey. The three band together and travel to different Disney-themed worlds, sealing the hearts of the worlds to prevent more Heartless invasions. Along the way, they encounter a group of Disney villains, led by Maleficent, who is controlling the Heartless. Though they eventually defeat Maleficent, the three discover that a man named Ansem is the true antagonist. Ansem's plan is to open the door to "Kingdom Hearts" in the hopes of attaining eternal darkness. Sora, Donald, and Goofy defeat Ansem, and seal the door with the help of Riku and King Mickey on the other side of the door.
After sealing the door to Kingdom Hearts, the three begin searching for Riku and King Mickey, finding themselves heading towards a mysterious fortress called Castle Oblivion. Upon entering the fortress, they begin to lose their memories. The three encounter a group of dark hooded villains, part of a mysterious Organization. In the castle, Sora learns his memories have been manipulated by a girl named Naminé who was being held captive by the Organization. To allow them to regain their memories, Naminé puts Sora, Donald, and Goofy to sleep for a year; in the process, they must lose the memories of their experience in Castle Oblivion. At the same time, Riku finds himself in the basement of the castle and begins traveling to the first floor with the aid of King Mickey. Riku fights both the Organization's members and the darkness in his heart, learning to accept his dual nature between light and dark. Allying himself with the mysterious DiZ, Riku aids him in keeping Sora and Naminé until the former is awaken. However a snag in the plan over the year forces Riku to go after a young man named Roxas, the thirteenth member of the Organization to enable Sora's reawakening.
Seven days after Riku's success, Sora, Donald, and Goofy awaken in Twilight Town, with no memory of their time at Castle Oblivion, and resume their search for Riku and King Mickey. They learn of the Nobodies and are re-familiarized with their leaders, Organization XIII. Afterwards, Maleficent is resurrected and joins with Pete, another Disney villain, to find a new base of operations before resuming her quest for power and revenge on Sora. Sora once again travels to many Disney-themed worlds and resolves the troubles caused by not just Maleficent and Pete, but also Organization XIII whose members refer to him as Roxas. Meanwhile, Kairi is kidnapped by the Organization. They meet King Mickey, who reveals that the "Ansem" Sora defeated was actually the Heartless of Xehanort, a student of the real Ansem the Wise and effectively the man whose body was possessed eleven years ago by Master Xehanort. Xemnas, the leader of Organization XIII, reveals himself to be the Nobody of Xehanort. The three arrive at the headquarters of Organization XIII, with Kingdom Hearts looming overhead, with Sora defeating all the Organization members as he is finally reunited with Kairi and Riku, who reveals Roxas as Sora's Nobody whom he captured by willingly assuming Xehanort's form so Roxas would be integrated back into Sora. While this occurred, Mickey finds DiZ, revealed as Ansem the Wise, with a device to digitize some of Kingdom Hearts' power, but a system overload causes the machine to explode with Ansem consumed in the blast as the others arrive, with Riku restored to his original state. At the top of the castle, Sora and his friends battle Xemnas, who uses the remnants of Kingdom Hearts to fight them. Refusing to accept defeat, Xemnas separates Sora and Riku from the others to fight them in a final battle that ends with his demise. Though trapped on the other side, Sora and Riku are able to return to their world.
Appearing the series prequel, Kingdom Hearts: Birth by Sleep, Kairi, Riku and Sora respectively encounter three figures named Aqua, Terra, Ventus. As the three children go on their lives, eventually meeting each other, the three figures they meet suffer horrific fates that indirectly influence the three children and what they will endure nine years later: Terra's body is stolen by the rogue Keyblade Master, Xehanort, transforming him into the Xehanort who will become Sora's greatest enemy; Aqua trapped in the Realm of Darkness; and Ventus, following a victorious mental struggle against his dark side, Vanitas, is left with a damaged heart which finds its way into Sora's body, leaving Ventus in a comatose state within the Chamber of Wakening. Back in the World of Darkness, Ansem encounters Aqua one year after Kingdom Hearts II as they now wait. Sometime later, Sora, Riku and Kairi receive a message from King Mickey, the contents of which detail his findings in Kingdom Hearts coded: Sora is destined as the "Key that Connects Everything" to save Terra, Aqua, and Ventus, as well as Roxas, Axel, Xion, and Namine. So Sora prepares to set out to find them.
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