X (エックス, Ekkusu?) is a manga series created by Clamp, a creative team made up by Satsuki Igarashi, Ageha Ohkawa, Tsubaki Nekoi, and Mokona.

X is Clamp's foray into apocalyptic fiction. It combines elements from various end of the world scenarios, both secular and religious, with its own mythos. The story takes place at the end of days, in the year 1999. The series follows Kamui Shirō, a young esper who returns home to Tokyo after a six-year absence to face his destiny as the one who will determine humanity's fate. The series is intended for a female audience, so X is drawn in the ornate style characteristic of shōjo manga but with the emphasis on moral conflict and gruesome violence expected of seinen works. The story is influenced by the works of Go Nagai and Kyokutei Bakin.

The unfinished series spans 18 collected volumes and five uncollected chapters. The manga was serialized in Kadokawa Shoten's Monthly Asuka from May 1992, until the magazine's editors showed concern with the increasingly violent stories and stopped publishing it on March 2003. X has since been translated into English, Portuguese, Chinese, French, German, Indonesian, Italian, Korean, Polish and Spanish and adapted into a series of audio dramas, an animated feature film and television series.

Source: Wikipedia