Crimson Viper, or C. Viper for short, is a secret agent from the Street Fighter franchise and appears in Marvel vs Capcom 3: Fate of Two Worlds, thus being a recently created character by Capcom this is the first crossover game in which she appears.
Crimson Viper , also known as Maya, is an American fighter employed by S.I.N., and presumed head of the "Battle Suit" Project. In reality, Crimson Viper is a secret agent under the employ of a U.S. government agency, presumably the CIA. She enters and participates in the latest world tournament under the guise of acquiring data for the Battle Suit for S.I.N., though her true motives are to acquire data from the BLECE Project (Pronounced Blees), in addition to eliminating "Number 15." (Seth)
If successful, she will be reassigned to the BLECE project. In addition to this, she's also to scout for potential recruits on a recruitment list she is given, one of whom is Hakan whom she rejects as a candidate. Prior to the tournament, Viper attacked Ryu under Seth's orders to test his skills, but the fight is interrupted by Cammy; Viper tortures Cammy in an attempt to force Ryu to access the Satsui No Hado, but is forced to flee when his power surges beyond its predicted levels. Before the tournament, she is informed that members of a C.I.A. team which was investigating S.I.N.'s rumored links to Shadaloo have all been assassinated. Realizing that she alone must finish the mission, she infiltrates S.I.N.'s HQ searching for information. While there, she comes across a wounded Seth, who recognizes her as a CIA agent. She responds by finishing him off. Unfortunately the data pertaining to BLECE is destroyed by Cammy before Viper has a chance to copy it, resulting in several years of investigation disappearing into thin air. The data linking Shadaloo to S.I.N. is not destroyed, however, and is recovered by Chun-Li prior to the Facility's destruction. Returning back to the CIA, she reports to her superiors that "#15" (i.e. Seth) has been eliminated, and that the "remaining 26" are in her sights.