It is within the time of Kingdom hearts I's beginning...However, this story does not unfold in the same way, there is no hero who travels from a small island to fight off the darkness... ... He's missing.
There are dark beings from the future, coming back to change history in their favor, they have begun to corrupt many timelines, many spaces in history, it is not long before all of time itself is enveloped by darkness...
But all is not lost.
The world created by the Keyblade war hero - Cyrus, is known as the Endless realm, he created it long ago, and from thus it split off from time itself, becoming an anomaly, his sword, The Kingdom Key...It rests inside of his castle within the Endless realm, it has been awakened by the corruption of history, the ebbs of time slowing to a halt, it cannot rest any longer, it has begun calling worthy heroes of all kind and creed, hoping they will hear it's cry, it must gather as many mighty fighters as it can, using the windows into time available within the Endless realm to send these heroes across many events and places in time, hopefully purging the darkness cast out in attempts to destroy everything. It is all up to those heroes, the Kingdom Knights, to destroy the source of all corruption.
But there are those will will resist. Those who will accept the destruction of time as they are consumed by the dark inside of their very own hearts, these people will fight to ensure their future is as bleak as their outlook, the Kingdom Knights will not face little opposition, much to the Kingdom Key's fears. But there are so many more as well. Countless Heartless of many types, all seemingly growing in intelligence, Nobodies, those which should not be searching the universe for their selves this soon, many things, many beings, all fighting for control over existence.
There will be many trials, many hardships, many friendships, and many learnings in this story, all shared by the evil, the good, and the neutral. This is where your story comes in, to merge with those of others, will you be a hero and bring light into history? Or will you seek to watch it fall? It is all up to you now... Perhaps you will be something else entirely, perhaps this story will have branches from your existence, only time may tell, and yours is a time that will prove interesting, I have no doubt.