Short answers, pulled from the story.
Vincent Valentine is the main character in Dirge of Cerberus Final Fantasy VII. He was a silent optional party member in the original Final Fantasy VII and became the central figure of this third-person shooter released in 2006.
Deepground is a shadowy organization dedicated to awakening Omega, a creature capable of destroying the Planet. The group consists of genetically enhanced super soldiers known as the Tsviets and was originally controlled by microchips implanted in their brainstems.
Dirge of Cerberus Final Fantasy VII was released in Japan on the 11th of September 2008. The game was part of Square's Ultimate Hits lineup after being postponed from its initial 2005 schedule.
Masashi Hamauzu composed the soundtrack for Dirge of Cerberus Final Fantasy VII. The theme songs were written and performed by Japanese singer and actor Gackt, who also voiced the character G in the Japanese-language version.
Over 513,000 copies of Dirge of Cerberus Final Fantasy VII were sold in Japan alone. This figure was recorded three months after the game's release in August 2008.