Konami and Platinum Games have a number of DLC planned for Metal Gear Rising: Revengeance's single-player campaign, which are expected to expand upon its story and background.
According to the game's chief story writer Etsu Tamari, the DLC will allow you to play as the bosses Jetstream Sam and Blade Wolf, in missions that serve as prequels to the game's main campaign. The stories will allow players to explore the back-story and origins of both characters.
"We don’t directly explain why Sam works with Desperado in the main story. So that content goes a little bit more into detail on it. The Blade Wolf sub-story depicts a mission it’s running with Mistral before the encounter with Raiden. Both of them serve as prequels to their roles in the main game," said Tamari in an interview with Polygon, who also explained why Raiden needed a canine pal, Blade Wolf.
“I told people that a cyborg needs a canine partner, and I stood really firm on that. I had trouble figuring out what sort of position it would take in the game, and eventually I came up with the idea that Raiden would take over the ‘teacher’ role for Blade Wolf, the way that Snake was his mentor in MGS2.”
It's interesting that the game will allow you to take on the role of some of the game's most interesting characters instead of simply giving you more of the same with Raiden.