"Crisis Core: Final Fantasy VII (クライシス コア -ファイナルファンタジーVII-, Kuraishisu Koa -Fainaru Fantajī Sebun-) is an action role-playing game developed by Square Enix for the PlayStation Portable. The game is a prequel to Final Fantasy VII and is also the sixth installment in the Compilation of Final Fantasy VII. Production was overseen by Yoshinori Kitase, the director of the original Final Fantasy VII, with Hajime Tabata as the game's director and Tetsuya Nomura as the game's character designer.
The game mainly focuses around Zack Fair, a 2nd Class SOLDIER, and the events leading up to his destined demise. He meets many of the Final Fantasy VII characters, including Cloud Strife and Aerith Gainsborough, with whom he develops strong bonds. The game's storyline takes the player from the war with the Wutai to the events at Nibelheim, and right up to the time just before the Final Fantasy VII beginning. Some of the missing events or plot holes from Nibelheim and afterwards are explained in the animated feature, Last Order: Final Fantasy VII."
Source: Wikipedia, "Crisis_Core:_Final_Fantasy_VII," available under the CC-BY-SA License.