A character within Kingdom Hearts 358/2 and has breif appearances in other games within the Kingdom Hearts series afterwards. Her anagram, No.i means No, as in nothing. The i does not reference the number I in roman numerals meaning 1 as many think, but the imaginary number i, meaning no number.

She takes the form of many people connected to Sora, taking the appearance of herself to many characters, Sora to Xemnas, and later Roxas just before her death, Ventus(Ven) for Xigbar, and a hooded puppet to Saix.

After dying in 358/2 Days, she has made a small appearance in Birth by Sleep during the secret ending and Re:Coded. Her most recent appearance was in the 3D trailer, where she is shown holding her Keyblade up to Roxas in CGI graphics.

Inside the fanon she is one of the most debated characters in the fandom. Many debate her existance in the fandom, calling her a Sue.
1)She weilds a Keyblade
2)She's the 14th member of Organization XIII
3)She's a replica of Roxas with Sora's memories looking like Kairi
4)She is able to destroy Akuroku and Soriku(explained later)

Xion is also paired with many characters in both het and Yuri pairings. Namely:
Roxas/Xion
Axel/Xion
Riku/Xion
Larxene/Xion

Many Yaoi fans and pre-358/2 game players are against her existance in the game, and she is both loved and hated by all fans. Everyone has different opinions on her role in the game.