I couldn't miss the chance to practice my drawing!
Twelve years ago... It was twelve years ago that the thing that connected our world with Wonderland, the Pillar of Darkness, first appeared. And then came Gun Dragon, and Sword Dragon...
The Day of Conjunction (界列の日, Kairetsu no Hi?) is a significant incident that occured twelve years prior to the events of Final Fantasy: Unlimited, and is further explained in Final Fantasy: Unlimited Before.
Primarily, it marked the destruction of Windaria and the appearance of the Pillar of Darkness on the Sea of Japan, in Earth.
Afraid of the existence of the Unlimited, Chaos deceived the inhabitants of Windaria and Misteria and made them fight each other. At some point, he destroyed Misteria and then attempted to consume Windaria. Chaos descended from the skies, throwing the world into disarray, just as he had done with Misteria before. The Windarians tried to fight it: the Moogles became Soil, but they were blown away by gales, and the warriors of the wind were annihilated by Chaos. Of them, only the Unlimited Kaze and the Moogle Pepo remained.
While pondering what they should do, an Unlimited and the only survivor of Misteria appeared, Makenshi, bringing Kaze his unconscious, but uninjured younger sister, Aura. He had saved her from being devoured by Chaos. Although they found it suspicious, Aura woke up and vouched for Makenshi. She then offered to sacrifice her life to become Soil, as did Pepo, so that Kaze could charge the Magun and evoke the ultimate summon. Completing the the Soul Charge Triad (Tear Rainbow, Soul Gun Metal) with his own soul (Endless White), he asked Makenshi to fire the Magun into Chaos, and destroy it with the Gun Dragon.
Unexpectedly, Chaos was not killed; rather, it assimilated the Gun Dragon and turned it red. However, Kaze's consciousness kept it at bay while Makenshi, turned into the "Symphony of the White Cloud" Sword Dragon, attempted to destroy it.
At the same time, the Pillar of Darkness appeared over the Sea of Japan on Earth, much to the astonishment of those who witnessed the event—among them, a young Lisa Pacifist, and the scientists Mary and Joe Hayakawa. Before long, the Chaos Gun Dragon passed through the Dark Pillar; military assets attempted to destroy it to no avail, until the Sword Dragon appeared. Finally, the dragons blasted each other out of the sky; however, rather than dying from the battle, Makenshi and Kaze survived. The latter was separated from Chaos, slipped into a coma-like slumber, and ended up in Wonderland.
In the aftermath of the event, Joe and Mary Hayakawa found two baby children, who were a part of Chaos that had split from the main body for unknown reasons. As Mary had lost her unborn child, they adopted the twins and named them Ai and Yu, but hid the truth from them and raised the two as normal humans.