[84] The series starts with Kingdom Hearts, where a boy named Sora is separated from his friends Riku and Kairi when their home Destiny Islands is consumed in darkness.

Though Sora defeats Ansem, he is forced to trap Riku and Mickey in the Realm of Darkness after sealing the door and resolute to find them while Kairi remains at the Destiny Islands for their return.

After Marluxia's defeat, the three are placed in a year-long sleep by Naminé to restore their original memories while losing their experience in Castle Oblivion.

Finding the comatose Sora while joining forces with the mysterious DiZ, Riku helps Naminé keep his friend safe until he is awoken.

In Kingdom Hearts II, after Roxas was integrated back into him, an awakened Sora and his friends resume their search for Riku and King Mickey, the latter's mentor Yen Sid re-familiarizing the trio with the Nobodies and Organization XIII's remaining members whom they deal alongside Maleficent and her right hand Pete.

Axel's action only give Saix, his former friend and Xemnas' enforcer, leverage to force Sora into finishing what Roxas and Xion began.

Axel sacrifices himself to help Sora's group reach The World That Never Was (Organization XIII's headquarters) and, after defeating Xemnas's right hand Xigbar, reunite with Riku and Kairi.

DiZ, revealed to be the real Ansem, attempts dissipating some of the artificial Kingdom Hearts before being engulfed in an explosion when his extraction device self-destructs and is sent to the Realm of Darkness.

[94] 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.

The letter, written by Mickey during the events of Kingdom Hearts Coded, describes the parts of their past that Naminé learned while restoring Sora's memory.

[98] To combat the new threat Xehanort poses, Sora and Riku take an exam to attain the Mark of Mastery that will allow them to become Keyblade Masters themselves.

[99] During the test in Kingdom Hearts 3D: Dream Drop Distance, Sora and Riku enter the Realm of Sleep where they encounter a young version of Xehanort who can travel through time.

[100] The two Keyblade wielders also learn how Xehanort has long manipulated events since Birth by Sleep with Organization XIII's true purpose in providing thirteens vessels for him to inhabit and use against seven hearts of pure light in an ultimate battle to recreate the χ-blade.

[101][102] But Sora's interference forced Xehanort to retrieve his alternate selves, Marluxia, Larxene, Demyx, Luxord, Vanitas, and Xion from across time in Replica bodies to form his ideal Organization XIII with Xigbar, Saix, and Vexen.

[104] At the end of the exam, Riku is declared a Keyblade Master;[105] in Kingdom Hearts HD 2.8 Final Chapter Prologue, Sora embarks on another journey to regain his "Power of Waking" while Riku helps Mickey find Aqua, Yen Sid training Kairi and Lea so they can help in the final battle against Xehanort and keep him from the Princesses of Heart.

[106] In Kingdom Hearts III, Sora regains his "Power of Waking" in his group's travels while Riku and Mickey retrace Aqua's steps to find her and Terra.

Once Aqua is purified by Sora and Riku, she leads them to Castle Oblivion which she restores to its true form as the Land of Departure to revive Ventus despite Vanitas' interference.

Afterwards it is revealed that Saix and Vexen sabotaged the Organization's plan by restoring Roxas as Sora's group manage to defeat all of Xehanort's remaining selves while freeing Xion and Terra from his control.

The games are driven by a linear progression from one story event to the next, usually shown in the form of a cutscene, though there are numerous side quests available that provide bonus benefits to the characters.

The games are influenced by their parent franchise, Final Fantasy,[109] and carry its gameplay elements over into their own action-based, hack-and-slash system.

[115] The main theme songs for the Kingdom Hearts games were written and performed by Japanese pop star, Hikaru Utada.

Each song has an English counterpart, "Simple and Clean", "Sanctuary", and "Don't Think Twice" respectively, for the North American and European releases.

After Kingdom Hearts executive producer Hironobu Sakaguchi told Nomura the game would be a failure if it did not aim for the same level as the Final Fantasy series, he began to develop the story further.

[176][177] By the end of March 2006, the NPD Group reported that Kingdom Hearts II was the highest-selling console game in North America, with 614,000 copies.

Both Square Enix and Disney have released a wide variety of Kingdom Hearts merchandise including toys, figurines, clothing, and jewelry.

[201] Sora has made guest appearances in other video games, including World of Final Fantasy and Super Smash Bros.

As of April 2019, a fifth series based on Kingdom Hearts III has been serialised monthly in Gangan Online with Amano returning to do story and artwork.

[206] Yen Press also licensed the series and published it online in English on apps such as Comixology and BookWalker alongside the Japanese release.

The cast of the games reprised their roles for the pilot with the exception of Haley Joel Osment, who was unavailable due to scheduling conflicts and was replaced with Bobby Edner.

[219] In October 2007, a fan-made web series of CG action films called Dead Fantasy was created by late web-based animator and writer, Monty Oum.