Χ series

The χ series (χシリーズ) is a series of titles in the  series that are primarily set in the ancient past, during the "age of fairy tales" and up to Xehanort in his youth and his journey to becoming a seeker of Darkness.

The series is followed by the Dark Seeker Saga.

Beginning
This storyline covers all games that canonically take place before Kingdom Hearts Birth By Sleep, sometimes referred to as "the age of fairy tales". Long ago before the Keyblade wielders, a war was fought between the physical manifestations of light and darkness for countless eons to finally end the conflict Darkness freed it's physical form however in doing so the one drawback was as a whole it's will couldn't be maintained nor survive without a host. By infecting others the darkness gave birth to creatures of darkness the Pureblood Heartless. To combat them it began the rise of the first wielders.

The Early Keyblade Wielders
This era was a golden age for them where the world was whole and light prevailed. Then one of the eldest Keyblade masters, Master of Masters trained apprentices of his own the foretellers and each formed their own guilds to bring order the increasingly chaotic and fragmented world. To aid in their endeavors the Master created the first Dream Eaters the Chirithy. However, thanks to the Nightmare Chirithy this era was soon wrought with turmoil and destruction due to the introduction and influence of darkness on the young and impressionable warriors, which culminated in the Keyblade War. Many innocent souls lost their lives, though the art of Keyblade wielding continued for some time after the dust settled. As it was the master's ulterior motives to set everyone else up first using himself and his apprentices to seal seven of the thirteen darknesses away from within.

The Union Leaders
Those that fled from the war became a separate group called the Dandelions. Five of them became Union leaders as they were the only ones to remember the past. To further bury the past the leaders created new dream eaters called Pet to aid the wielders themselves in their new adventures reuniting with old and meet new friends and enemies. However just like the Foretellers, the Master knew that the remaining darknesses continued to follow them and it was his intentions to trap five of them within the young leaders and the last one in the data world itself. But thanks to Darkness interfering and yet the brave sacrifices of valiant friends most of the Union leaders escaped to parts unknown and the remaining dandelions eventually met a grim fate and were forced to sacrifice themselves to become Dream Eaters.

Xehanort's Early Years
We learn of Xehanort's life before he became a dark seeker before Player's demise they connected their hearts with him as a baby and was sent away for unknown reasons to Destiny Islands. Growing up, he was plagued by dreams of Player's memories and wished to under there meaning and thanks to his future self; Xehanort returned to his homeworld Scala ad Caelum, trains to become a Keyblade master alongside with Eraqus and his other apprentices. After many tragic events, including the deaths of many of his friends, his heart was broken and corrupted by darkness. After meeting a time traveling Ansem, he is explained about his future plan to summon the seven pieces of light and thirteen pieces of darkness to reforge the χ-blade and summon the true Kingdom Hearts. He spent the next several decades study about the history and workings of Keyblades, as well as the Heartless, Nobodies, and the process of recompleting. This all culminates in him discovering Terra, Aqua, and Ventus, as he wishes to use them and their insecurities to do his bidding and forward his master plan.