-- are what I love the most about Chief's characterization in the game.

Obviously this theory might have a few plot holes in it. But it never left my mind ever since the Underground Shepherd referred the Chief as their sibling. So I guess feel free to take apart this theory of mine.

'Till next time.

So I thought that what if instead of waiting for a Black Ring to naturally show up (like Phantom Hamel), the Underground tried to artificially kickstart a Black Ring with the 'perished' Shepherds in Lone Island?

But why was the defect the only specimen of the shackles that the FAC was able to retrieve? Why not every one?

Well, something must have happened to them during that operation. Since only the Chief and the Underground Shepherd has the ability of to conjure shackles.

In Flora Unfurl, it was revealed that an operation was conducted by the Paradeisos and FAC to obtain something from the Underground, ten years prior to the start of PtN.

It was revealed that their target was the Chief, the defect.

The Deus Corpus from BR-04 that was composed of both Earl and Zoya, has revealed that the Chief was a defect. The Chief is constantly refered as a defect by both the Underground and Paradeisos. So how can the Deus Corpus know it even though it hasn't been told to them by the Underground agent?

My theory is that, the Deus Corpus are actually the other Shepherds created by the Underground in Lone Island.

Why do I think that?

In order to not spoil too much, I'll just say that the Deus Corpuses have all expressed familiarity with the Chief, or specifically the shackles.