*BIG SPOILERS! READ AT YOUR OWN RISK!*
The events of Metal Gear Rising: Revengeance are set four years after the events of Metal Gear Solid 4: Guns of the Patriots.
The Patriots, a powerful shadow organisation running the world's war economy, have been destroyed and Private Military Companies (PMC) have splintered into numerous factions. With the elimination of the Patriot-controlled nanomachine technology used to regulate soldiers' abilities, PMCs turn to advanced cyborg technology, creating durable superhuman soldiers.
You control Raiden, a former child soldier turned into a cyborg that now works for the PMC Maverick Securities. Raiden is supported by his Maverick colleagues, Russian pointman Boris Popov, military advisor Kevin Washington, computer specialist Courtney Collins, and cybernetics expert Wilhelm "Doktor" Voight. Returning from Metal Gear Solid 4: Guns of the Patriots is Sunny, a member from the company Solis that is a friend of Raiden.