The Wielder’s objective is to collect light known as Lux, and to prevent the creatures of the dark, known as the Heartless, from contaminating the worlds with darkness. Eventually, a feline creature named Chirithy befriends the Wielder and elaborates on their role.
Before the Wielder strikes back, the Union leader of the player’s chosen faction arrives to intimidate the creatures of the dark away. After the Wielder chooses their Union, they are entered into Daybreak Town, and are attacked by creatures of the darkness who have entered through a portal. This Keyblade Wielder gets the choice of choosing one of five Unions to pledge their loyalty to: Unicornis (ruled by Master Ira), Anguis (ruled by Master Invi), Leopardos (ruled by Master Gula), Vulpeus (ruled by Master Ava) and Ursus (ruled by Master Aced). Kairi’s grandmother tells Kairi about the tale of Light and the Darkness during the age of fairy tales, in which the story gets reinacted through a bespoke Keyblade Wielder. Kingdom Hearts χ begins through a pop-up book, which display’s Kairi and her grandmother in Radiant Garden.
Naturally, there will be significant spoilers up ahead. Given how difficult it can be to follow the lore of the series, even now that it's begun consolidating titles and releasing past Kingdom Hearts titles across new platforms such as PC, anyone who hasn't played through or watched previous KHUX story updates should probably do so before diving into its ending, which wraps up plotlines that were established much earlier on in the mobile game's life. Related: Looney Tunes Deserves Its Own Kingdom Hearts-Style Game
Kingdom Hearts Union X takes place before any other entry in the franchise, set in the era before the Keyblade War so it can establish the backstories of characters who would become important in other Kingdom Hearts games. Some games exist just to set up or flesh out events that take place in earlier-released titles, such as 2010's Birth By Sleep, precursor to 2002's Kingdom Hearts. Kingdom Hearts is known for having a convoluted story with a vast and interconnected timeline. For the moment, here's a general overview of how Kingdom Hearts Union X's story concluded.
In it, several loose ends that tied into other parts of the series were finally resolved, but there are still quite a few questions left up in the air, and it seems like Kingdom Hearts fans will have to wait for future games in order to get concrete answers.
One of the mobile titles in the Kingdom Hearts series, Kingdom Hearts Union X ( KHUX), received its final story update back in May in Japan.