To Unlock Monster Hunter Missions within the game, first listen to all of Chico's Briefing files library. You can skip through these all with Circle; just make sure that the exclamation marks are all gone. These can only be unlocked after completing the mission within the area. This includes:River Valley - Mission 5
Crater Area - Mission 8
Tropical Cloud Forest - Mission 10
Ruins - Mission 13
Mine Base - Mission 15
- The Loch Ness Monster
- Mokele Mbembe
Once that has been done, start either Extra Mission  or , with Snake. When it has loaded, proceed to Playa del Alba and make your way onto the pier after receiving a codec call from Kaz. A cutscene will then start, and afterwards you will have unlocked your first Monster Hunter mission!