Similar to the Hazardless form of Smashville, the fighting area is a medium-sized platform with a lone smaller one floating above the very center. Much like Northern Cave or the Omega and Battlefield forms of Delfino Plaza and Skyloft, the stage flies around Hollow Bastion, first starting at the Rising Falls, before gradually making its way near the front exterior of Hollow Bastion's castle to show off its details.
If Time is running out, or players are at their last Stock, the stage transitions into an alternate form known as Dive to the Heart; while the layout remains the same, its design undergoes a dramatic overhaul, with the background now randomly showing one of seven Stations of Awakening:
- Sora's station, featuring Riku, Kairi, a Paopu Fruit (replacing Donald Duck), and the Highwind (replacing Goofy). The background depicts Destiny Islands, and the ring bears the Crown symbol often associated with Sora.
- Riku's station, featuring Sora (replacing King Mickey), Naminé, and Ansem, Seeker of Darkness. The ring features the Cards from Kingdom Hearts: Chain of Memories.
- Roxas' station, featuring Riku (as he appears in 358/2 Days), Xion, and Axel. The background depicts Twilight Town and the ring bears the Nobody emblem.
- Xion's station, featuring Sora, Axel, Saïx, and Xemnas. The background depicts Where Nothing Gathers and the ring bears the Nobody emblem.
- Ventus' station, featuring Wayfinders. The background depicts the Keyblade Graveyard and the ring bears Terra's emblem.
- Terra's station, featuring Ventus, Aqua, and Wayfinders. The background is a checkered pattern bearing the Heart, Crown, and Unversed symbols, with the ring having an alternating pattern with a Wayfinder and Terra's own emblem (replacing the Mickey Head symbols).
- Aqua's station, featuring Ventus, Terra, Vanitas, and Xehanort. The background is also a checkered pattern with the Heart, Crown, and Unversed symbols (replacing the Mickey Head symbols), and the ring bears a Wayfinder.
As with all Battlefield and Omega forms in Ultimate, the stage has been reshaped to resemble the game's Battlefield and Final Destination. The background sequence will play virtually unchanged in either form, as well the conditions that transition into the Dive to the Heart form.
Hollow Bastion is the penultimate world in the first Kingdom Hearts. In the story, Riku is transported to the Rising Falls after Destiny Islands' destruction where he meets Maleficent, who offers him a place to stay in the world's castle. Later in the game, after all of the Disney worlds have been visited and saved, Sora, Donald, and Goofy arrive at Hollow Bastion and reunite with and confront Riku as he is facing off against The Beast from Beauty and the Beast, who has infiltrated the castle to find Belle. Riku declares himself to be the true wielder of the Keyblade, forcing a conflicted Donald and Goofy to follow him as they were ordered to follow the Keybearer, leaving Sora and The Beast to team-up and navigate their way up the castle. Later, Maleficent attempts to open the Bastion's Keyhole with the Seven Princesses of Heart, but can't as Kairi's heart is still required. Sora and his party eventually confront Maleficent and defeat both her human and dragon forms before confronting Riku again, having now been possesed by Ansem, Seeker of Darkness. After Ansem-Riku tells Sora that Kairi's heart has been residing within him and defeats Xenahort's Heartless, Sora tries to seal the Bastion's Keyhole but is unable to due to it being incomplete; Sora realizes that he must free Kairi's heart hiding within him, and decides to willingly stab himself with Riku's Keyblade of heart, freeing all Seven Princesses' hearts and completing the Keyhole. Kairi awakens and witnesses Sora succumbing to darkness and mourns with Donald and Goofy; Ansem tries to kill Kairi having deemed her purpose fulfilled, but Riku manages to regain control of his body to warn the group that a swarm of Heartless will take over the castle and instructs them to escape. During their fleeing, they run into a docile Heartless, to which Kairi quickly deduces is actually Sora. As the Heartless swarm their way into the Bastion, a bright light repels them, which has turned the docile Heartless back into Sora. The Beast returns to stave off the swarm as he continues to search for Belle, allowing Sora and his party to escape. Later, after defeating a Behemoth Heartless and with assistance from Cid Highwind and Squall Leonhart, Sora returns to Hollow Bastion to seal its Keyhole. In Kingdom Hearts Final Mix, Sora and his party can return to the castle to initiate a secret boss battle against a mysterious cloaked being only known as "Unknown" (later revealed to be Xemnas).
Hollow Bastion returns in Kingdom Hearts: Chain of Memories, this time as a memory simulation that both Sora and Riku enter. Riku finds himself in a simulation of his bedroom in the Bastion, where Maleficent tempts him into rejoining her side; he refuses and defeats her in a subsiquent battle. Sora and his party later arrive and are reunited with The Beast, who is distraught after hearing Belle tell him to stay away from her. They eventually encounter Maleficent, who has held Belle hostage and that the reason she pushed The Beast away was to avoid detection. Sora and his party battle with her dragon form again and eventually prevail, allowing Belle and The Beast to reunite.
Hollow Bastion later returns in Kingdom Hearts II, now serving as a hub world for Sora, Donald, and Goofy, acting as a replacement for Traverse Town from the first game. It is revealed that the world was the home for several Final Fantasy characters, namely Aerith Gainsborough, Yuffie Kisaragi, Cid Highwind, and Squall Leonhart who have since formed the Hollow Bastion Restoration Committee to restore their homeland; Squall makes Sora, Donald, and Goofy honorary members of the committee. It is also here where the party has their first encounter with Organization XIII, and where Sora is able to travel to other worlds via his committee card, allowing him to continue the party's search for Riku and King Mickey. As the game progresses, more denizens and locations are revealed, including the likes of Tifa Lockhart, Merlin (in possession of the book that leads into the 100 Acre Wood), and Cloud Strife who is looking to challenge Sephiroth. It is also here where Sora learns the story of Ansem the Wise. Later, Maleficent invades the Garden with a swarm of Heartless and Nobodies, but is successfully fended off by Sora and his allies; however, Maleficent betrays Organization XIII and attempts to claim Kingdom Hearts for herself. Much later in the game, the Master Control Program takes over Cid and Ansem the Wise's computers to malfunction, causing the Bastion's claymores to attack the residents. With the help of Tron, Sora and his party are able to regain control of the computers, as well as uncover hidden data on the world's former existance as Radiant Garden; this would later be expanded upon in Birth By Sleep as a beautiful landscape overseen by Ansem the Wise, who ruled in the Hollow Bastion castle that would later be remodeled to include mechanical parts after Xenahort overthrows Ansem the Wise from the throne, turning it into the distorted castle that it appears in the first game while most of the residents escaped to Traverse Town. Radiant Garden wouldn't be fully restored until the events of Kingdom Hearts III.
Dive to the Heart is a recurring area in the series, often depicted as a metaphysical place set in a dream. It is said to be a representation of the person's heart and (in the case of Sora, Roxas, and Ventus) can only be reached by diving into the ocean. The area consists of giant pillars adorned with stained glass window designs, which are called Stations of Awakening; the tops of the pillars the characters are meant to stand and walk on depict a specific set of characters that usually have a strong connection with each other. Gameplay wise, it serves as a tutorial area where the player can learn the controls and battle the first boss.
- All of the Stations of Awakening are taken from official merchandise that was made to commemorate Kingdom Hearts' 15th Anniversary, all of which remove any imagery relating to Disney characters or iconography.
- Hollow Bastion is the only stage to transform permanently and the only one to do so under a specific condition.
- Sora's Station of Awakening cannot appear when he is on the stage.
- Dr. Kawashima is the only Assist Trophy that will not appear on the stage. Lunala is also the only Poké Ball Pokémon that will not appear.