The series starts with Kingdom Hearts showing how a 14-year-old boy

The series starts with Kingdom Hearts showing how a 14-year-old boy named Sora is separated from his friends Riku and Kairi when their world, Destiny Islands, is invaded by creatures known as the Heartless. During the invasion, Sora obtains a weapon called the Keyblade that allows him to fight the Heartless. He soon arrives in another world, Traverse Town, where he meets Donald Duck and Goofy, two emissaries from Disney Castle sent by King Mickey to find the wielder of the Keyblade.[65][66] The three band together and travel to different Disney-themed worlds, sealing the hearts of the worlds to prevent more Cosplay Costumes Heartless invasions, and to find Riku and Kairi. Along the way, they encounter a group of Disney villains led by Maleficent, who are controlling the Heartless to capture seven maidens called the "Princesses of Heart", and use their power to open the door to "Kingdom Hearts" and rule over all the worlds.[67][68] Though they eventually defeat Maleficent, the three discover that Ansem has been possessing Riku's body and using Maleficent, and plans to attain eternal darkness by opening Kingdom Hearts himself. Sora, Donald and Goofy defeat Ansem, and seal the door to Kingdom Hearts with the help of Riku and King Mickey on the other side of the door. Kairi remains back home to await her friends' return.

In Kingdom Hearts: Chain of Memories, Sora and his two friends begin searching for Riku and King Mickey.[69] They arrive at a fortress called Castle Oblivion,[70] where they encounter members of a mysterious group called Organization XIII, which is made up of non-existent beings called the Nobodies. While in the castle, the three's memories are manipulated by Kingdom Hearts Costumes a girl named Naminé.[71] After defeating the Organization, the three are put to sleep for a year by Naminé to allow them to regain their memories, though they must lose the memories of their experience in Castle Oblivion.[72] Meanwhile, Riku appears in the basement of the castle and travels up to the surface with the aid of Mickey. Riku then keeps Sora and Naminé safe until Sora is awoken. In Kingdom Hearts 358/2 Days, a snag in the plan over the year forces Riku to capture Roxas, the thirteenth member of the Organization, in order to enable Sora's reawakening.

In Kingdom Hearts II, Sora and friends awaken from their sleep and resume their search for Riku and King Mickey, passing through Twilight Town and meeting Yen Sid, learning of the Nobodies and becoming re-familiarized with Organization XIII. Sora once again travels to many Disney-themed worlds and resolves the trouble caused by the Heartless and Cosplay Costumes Nobodies, and Maleficent's servant Pete. They reunite with King Mickey and encounter Xemnas, the leader of Organization XIII.[73][74] The Organization's plan is also revealed—they seek the power of "Kingdom Hearts", the sum of all the hearts that Sora released by destroying the Heartless with his Keyblade, to regain their lost hearts. The three arrive at the headquarters of Organization XIII and team up with their friends and Kairi, who went to find Sora earlier. Ansem the Wise uses a device that dissipates some of Kingdom Hearts' power,[75] but it self-destructs, engulfing Ansem. At the top of the Castle that Never Was, Sora and his friends battle Xemnas.[76] After Sora and Riku defeat Xemnas, they get trapped in the Realm of Darkness, but a letter from Kairi summons a gateway for them, and the two are reunited with their friends at their home.