To unlock the mission, you need to make sure you have done this steps:
- Spare the life of Quiet at end of Mission 11 so that you can recruit her as a “Buddy”.
- Make sure you have the maximum possible bond with Quiet. You can check it out during the mission selection screen.
- You have seen the cutscene at Mother Base in which Huey is exiled.
- You don’t use the “Butterfly” design for your emblem.
Now the final process has been started (See spoiler on how to prevent this).
You can start Side Op 150 now. By progressing through this mission you will collect a file, which immediately starts the main mission 45. The achievement pops after completing this.Important:
(Decide if you want to know it, but I think you should)