You need to collect 11 Photos to unlock this Secret Achievement. Every Wandering MB Soldier (Extract the Wandering Motherbase Soldier’s SideOps) has a Photo with him. After you completed one Mission (or if you’re at Motherbase anyway) go to the 2nd Level of the Medical Platform and visit someone (MSG:GZ players won’t believe it). After that someone has seen all then Photos you collected you can find the last one just outside her Room on the Wall, left of the Exit – you can’t show that someone all ten Photos at once, you need to leave the MB every time.
Wandering Motherbase Soldiers hard to catch?
Play “koi no yokushiryoku” over your iDroid Loudspeaker or use a Cardbox 😀