Interesting details about Metal Gear Solid: Peace Walker's development were provided by Hideo Kojima. The PlayStation Portable game Metal Gear Solid: Peace Walker was released back in 2010. The original Metal Gear game carried on Big Boss's adventure as he formed his own mercenary group in Colombia, much like in Metal Gear Solid: Portable Ops. Although that wasn't the case when the game was launched, Kojima has acknowledged that it was previously the goal for the game to be the fifth main line entry in the series.

Hideo Kojima has told numerous stories about the creation of the portable game. One regret Kojima had regarding Metal Gear Solid: Peace Walker was revealed in a news report; it turned out that the song was something he had originally intended to include in the game. It appears that the well-known video game designer had more fascinating tales to tell about creating Peace Walker.

Hideo Kojima recounted a story about how Metal Gear Solid: Peace Walker was originally intended to be the fifth mainline game in the series on Twitter. When describing the game as MGS5: Peace Walker, Kojima stated that he intended for it to have a proprietary engine. Although Konami has since discontinued the Fox Engine, it was included in a number of the company's titles.

Kojima went on to explain that Peace Walker was meant to serve as a Metal Gear franchise transitional evolution while the engine was being finished. However, international marketing fiercely opposed the planned Metal Gear Solid 5: Peace Walker title. This is why the developers opted to delete the numerical title, while simultaneously lowering the target age range of eligible players. In the end, Metal Gear Solid 5 was released as MGS5: The Phantom Pain, which featured the intended Fox Engine. And while opinions on how Metal Gear Solid 5: The Phantom Pain was received have varied, many people think the fifth installment is a good game.

It's possible that there hasn't actually been a fifth game in the series as Kojima previously stated on Twitter that Metal Gear Solid 5: The Phantom Pain was intended to be read as Metal Gear Solid V. Perhaps Kojima still views Peace Walker as the fifth mainline game, even though Phantom Pain essentially rewrote the Metal Gear Solid formula. Furthermore, it is evident how important the game is to Metal Gear Solid's mainline chronology given that Peace Walker is allegedly included in Metal Gear Solid Master Collection Volume 2.