In most epic struggles, destiny and tragedy are the two primary ingredients. X is no different. Almost all action in the film does fits into the great work of fate and destiny that wraps itself around every single character in the story. The story is about a battle whose outcome will determine the fate of the Earth at the end of the millennium. It is about an Earth where there are six shields (Dragons of Heaven) and six destroyers (Dragons of Earth). Both sides are waiting for their seventh member who will either save or destroy the Earth. Even though these characters know their role in the drama, they do not realize the extent of what their fate is.
The story starts with Kamui being bidden to return to Tokyo as his fate demands by his mother. As a parting gift, she gives him a sword that costs her her life. Upon Kamui's arrival in Tokyo, both sides are alerted and they prepare their meeting with Kamui to draw him to their side. The final battle begins as soon as Kamui begins traveling through Tokyo.

The cast of the story has 18 characters. Kamui's mother is possibly the only person in the story who knows her and Kamui's role. Kamui, having been separated from his two most important friends for six years, is intent on returning to Tokyo to protect them from the impending doom. Fuuma, Kotori's older brother and Kamui's friend, has promised to protect Kamui if he protects Kotori. The young Kotori is a symbol of innocence and of the Earth itself.
Hinoto is the leader of the Dragons of Heaven; she guides them in their geas to protect the Earth. The Dragons of Heaven are: Sumeragi Subaru, Kasumi Karen, Nekoi Yuzuriha, Arisugawa Sorata, Aoki Seichirou, and Kishu Arashi.
The Dragons of Earth are lead by Kanoe, Hinoto's younger sister. Hinoto and Kanoe share a vision of the final battle of the Earth between the Dragons of Earth and the Dragons of Heaven. Kanoe believes that her interpretation of this vision is the more correct one. This hubris leads her down the path of playing with fire and ends up awakening Fuuma and setting him against Kamui. The Dragons of Earth are: Shiyu Kusanagi, Asagi Shougo, Sakurazuka Seishiro, Yatoji Satsuki, Rigai Yuto, and Nataku.
The two sides at first vie for the attention of Kamui, believing that he is the one that will complete their number and assure their victory in the coming battle. While this appears to be the primary struggle in the story, it is just the backdrop for the battle between Fuuma and Kamui. Two titans locked in battle due to an apparent misunderstanding: Kamui tries to protect what he can, his love paralyzing him against action. Fuuma lives in a world created possibly out of jealousy of Kamui and is intent on destroying him because of his failed responsibility towards Kotori.