Giant Bomb's Unofficial MGSV Group

Thanks to intrepid intel team member AdequatelyPrepared on GB, we've got a better understanding of how the FOB system actually works. Here's the relevant page[mgstpp-app.konamionline.com], but be careful browsing from there if you are very spoiler adverse as there may be some minor things on other pages that you won't want to see. Keep in mind this is the PS4's manual so there may be some irrelevant info.

Here's some highlights:

"FOBs you can infiltrate must either be in the same PF Grade bracket as you, be a rival who infiltrated your FOB in the past, or be the retaliation target of a PF you are supporting."

"If you can reach the core of the platform you have infiltrated, you will capture a large number of personnel from your opponent.
However, if your opponent's forces spot you, the user who owns the FOB may come and join the defense."

"You can earn rewards for successfully infiltrating or defending an FOB, besides the materials and personnel you steal from the opponent.

The rewards are even greater for successfully defending another user's FOB."

"Gain supporter PFs using [RELATIONSHIPS] in the iDROID's [MISSIONS] tab, and friendly users may come to help your defense."

It seems like we can add each other using the "RELATIONSHIPS" tab in the iDroid, which is how you choose which PFs (other players) you are supporting, and also how you share retaliation targets.

It's still unclear how that ties into the system level friends stuff (I.e. if everyone on your list will be under the RELATIONSHIPS tab), or there's any sort of cap (hope not!), but we'll know very soon. Either way, it seems we get a bonus for helping each other out versus going it alone, which is a smart way to incentivize it.