Gameplay involves players navigating a customized avatar through Disney-inspired worlds fighting enemies, along with taking down bosses in multiplayer matches in competition with other teams.

A version of the game for mobile devices called Kingdom Hearts Unchained χ was released as the ninth installment of the series in Japan in September 2015, and worldwide in 2016.

Players can customize the gender, hair, and clothing, and choose accessories themed after both Square Enix and Disney universes present in the Kingdom Hearts series.

[9] If the player's HP is fully depleted, a choice is offered between forfeiting all progress in the quest or continuing to fight by spending Jewels, a new general-purpose in-game currency.

[9] Kingdom Hearts χ is set in a world called Daybreak Town, hundreds of years prior to the other games in the series.

To prevent this, the Foretellers use their books to manifest future worlds and defeat the Heartless infesting them to gather pieces of light, called Lux.

The player character, a newly awakened Keyblade wielder, chooses to support one of the Unions and works to ensure the chosen faction's supremacy.

Due to the Book of Prophecies' loss of power without the Master or Foretellers present, the Keyblade wielders instead visit simulated datascapes based on the various Disney worlds.

New stories feature the player forming a new team with four other Keyblade wielders, who become friends, while a new set of union leaders must contend with new formless, sentient incarnations of True Darkness.

Upon her defeat, Ava reveals that she has recruited Ephemer into the Dandelions, a group of Keyblade wielders intended to be kept out of the impending war so they may rebuild the world in its aftermath.

Unbeknownst to them, Maleficent appears nearby – having traveled back in time after being defeated by Sora and his friends[c] – and makes plans to conquer her world in the past.

The Master entrusts Luxu with his Keyblade and a black box, which he instructs him to never open, revealing his plan to end a greater war against thirteen willful embodiments of True Darkness by using his apprentices and the new Union leaders as vessels to contain them.

Fearing the damage she could cause with her knowledge of the future, the Darkness instructs her to use a "lifeboat" pod within the tower in Daybreak Town to return to the real world.

Brain, Lauriam, Ventus, and Elrena use the remaining pods to return to the real world; Ephemer, Skuld and the player stay behind and protect the Dandelions until they can all be rescued.

Xehanort, living bored on the Destiny Islands, is approached by Ansem, his Heartless from the future, and is shuffled through a portal to Scala ad Caelum, a world where Keyblade wielders are trained.

Two years later, Xehanort – now a Keyblade wielder – and his classmates Eraqus, Urd, Bragi, Vor, and Hermod are told by their master, Odin, that seven upperclassmen have gone missing before their Mark of Mastery exam.

Xehanort and his friends eventually find Vidar, Vala and Vali, three of the upperclassmen, who have been stealing items essential to worlds' natural order.

Vidar explains that they learned of the thirteen True Darknesses from Odin, and that they now seek to purge the world of them by finding the seven pure lights needed to summon Kingdom Hearts.

While there, they find the souls of Hoder and her fellow upperclassmen – Heimdall, Helgi and Sigrun – learning that Vidar's desire to purge the darkness was to avenge their deaths.

[f] A post-credits scene shows a flashback to Xehanort's childhood, in which he is watched over on Destiny Islands by his elderly mentor, the reborn player from Union χ.

The mentor believes Xehanort to be the "child of destiny", a prophesied savior of the world, and has sequestered him there to hide him from the True Darknesses until he becomes strong enough to defeat them.

Kingdom Hearts χ was co-directed by Tetsuya Nomura, one of the series' creators, and Tatsuya Kando, who had previously directed Nintendo DS game The World Ends with You.

[16] Due to difficulties that arose adapting the core Kingdom Hearts experience into a browser game, the presentation was designed similar style of fantasy classics of the locations encountered previously by series protagonists Sora and Riku.

[18] Despite this strong link, it was described by Tetsuya Nomura as a title where story was not the focus, and that its content was completely separate from the main series, making it accessible for newcomers.

As mobile devices employ a different control set-up to web browsers, Unchained could not work simply as a port of Kingdom Hearts χ.

One of the changes instituted during the games mobile remake was to make the gameplay more "casual" than Kingdom Hearts χ, with battles being shorter and potentially easier.

To promote the game, codes for special items and in-game currency were included with first-print copies of Kingdom Hearts HD 1.5 Remix.

Square Enix also announced a subsequent update that would complete the story of Kingdom Hearts Dark Road and allow players to play it in its entirety offline, which was later released on August 26, 2022.

The collection features Kingdom Hearts χ Back Cover, a 60-minute cinematic film that focuses on the Foretellers, elaborating on their actions during the events of the game and their attempts to determine who is the traitor among them.

[38] Richard Eisenbeis of Kotaku was generally positive, saying that despite it being similar to other Japanese browser games and using a micro-transaction system, it was "an enjoyable little time waster.