Predictably, the tablet app will display the game's map for players on Xbox One. "How convenient!" Kojima wrote.
However, you'll also be able to use Snake's iDroid, his portable terminal device, from the tablet screen, Kojima revealed in another tweet. That certainly makes sense, though it's unclear exactly what role the device will play in-game. Inventory management, menu navigation, and even communication on the tablet screen are all likely, however.
In other tweets, Kojima confirmed that these features will be available on smartphones as well, and that MGS V will feature remote play for PS Vita owners.
Given that tablet companion apps are becoming a focus not just on Xbox but for PlayStation gamers as well, MGS V's second screen features will likely be available for more than just the Xbox One version. However, since Xbox One is the only platform that Kojima mentioned in his tweets, that's not confirmed.
Tablet companion apps for console video games have so far been disappointing, but if a really big game—like Metal Gear Solid V—can find a way to do it right, the second screen might finally be able to take off.