Grav!ty
Remember though, at that point Peace Walker was still officially considered MGS5.
...A minor correction.
Quote:
Kojima wrote, produced and directed the game, stating that the game was not a spin-off, nor was it a sidestory. Kojima referred to both Peace Walker and Metal Gear Solid: Rising as Metal Gear Solid 5, while specifically calling Peace Walker "the MGS5 inside me."
Prior to the announcement of Metal Gear Solid 5, the title was used by Hideo Kojima to refer to two seperate games in the Metal Gear series
Metal Gear Solid Rising, Kojima refers to it as the generation of MGS5.