Kingdom Hearts χ

Kingdom Hearts χ[chi] was a Japan-exclusive PC Browser game and the ninth mainline entry in the Kingdom Hearts series. The game is a prequel to the every Kingdom Hearts game to date, depicting the legendary "Keyblade War" mentioned in several other titles. Originally releasing in 2013, a mobile port/remake called Kingdom Hearts Unchained χ was released in 2015. The original browser version was shut down in 2016.

Relevance to Final Fantasy
Several Final Fantasy characters appear in this game.