X or χ (the letter "chi") may refer to:
- Chi and the Recusant's Sigil, which are symbols represented by an X.
- The χ-blade, a legendary weapon introduced in Kingdom Hearts Birth by Sleep.
- Kingdom Hearts χ, a Kingdom Hearts game exclusive to PC browsers.
- Kingdom Hearts Unchained χ, a Kingdom Hearts game exclusive to smartphones.
- Hunter-X, a powerful enemy ship in Kingdom Hearts II.
- Luxord, number X in Organization XIII.