X (disambiguation)

X or χ (the letter "chi") may refer to:
 * The χ-blade, a legendary weapon introduced in Kingdom Hearts Birth by Sleep.
 * The Recusant's Sigil, which is represented by an X.
 * Luxord, number X in Organization XIII.
 * Subject X, a mysterious girl first mentioned in Kingdom Hearts III.
 * The χ series, a subseries of Kingdom Hearts prequels.
 * Kingdom Hearts χ, a Kingdom Hearts game exclusive to PC browsers.
 * Kingdom Hearts Union χ, a Kingdom Hearts game exclusive to smartphones.
 * χ3, a community feature in Kingdom Hearts Union χ.