James Grayson developed a more personal hatred of the Chimera than most humans after he was forced to mercy-kill his own brother, Jonny, after he was partially transformed into a Hybrid at a Chimeran Conversion Centre. Although he is a member of the British Navy, throughout Resistance: Retribution he wears the flight jacket of the Royal Air Force; Jonny was a pilot and James adopted his brother's jacket after his death, to remind him at all times why he fought.
Retribution can be "infected" by the related game Resistance 2 via connection from the Playstation 3 to the PSP. This causes several modifications to the game, most notably the fact that this time, in James' backstory, he, like Nathan Hale, the protagonist of the main Resistance storyline up til that point, was partially infected by the Chimeran virus. This grants James the ability to breath underwater indefinitely, as well as the traditional health regeneration of the series, so he doesn't have to rely solely on health kits, as it is normally. In addition, it unlocks access to several weapons unavailable during the normal campaign, such as the Magnum pistol used by the Sentinels, and changes his physical appearance; his eyes have the golden glow of the infected, and he wears the uniform of the Sentinels, the elite squad of partially-infected soldiers from Resistance 2, instead of Jonny's flight jacket. Finally, infection also alters certain lines of dialogue to reflect James' new state.