Kingdom Hearts Birth by Sleep

Kingdom Hearts Birth by Sleep is the sixth mainline entry in the Kingdom Hearts series. The game is a prequel to all games released before it, explaining the various catalysts for the story archs expanded upon in those other games. Originally released on PlayStation Portable in 2010, the game was remastered in 2014 as part of Kingdom Hearts HD 2.5 ReMIX for PlayStation 3, which itself was remastered in 2017 as part of Kingdom Hearts HD 1.5+2.5 ReMIX for PlayStation 4.

Relevance to Final Fantasy
Several Final Fantasy characters make appearances in this game.