That suit looked very like a diver’s apparatus, which I thought was interesting given they also had him almost drown but mysteriously survive. There must have been some sort of magic in the suit that kept him alive in it for years, so maybe that magic was tied up in his underwater survival trick. Ability to slow down metabolism or something.
Anyway, I think the whole diver suit/drowning thing symbolizes the fear of going deeper.
Because I think at the beginning of the series, Cain had become a very bitter and unforgiving man. His first reactions to the others were very superficial and judgmental: If Glitch had a zipper in his head, he must have deserved it by being criminal, if someone was stuck in a Papay cocoon, they must have deserved it by being careless or stupid. Even using terms like ‘zipperhead’ suggests a certain cold disregard for feelings, DG never would have used the term in a million years.
I thought the comment that Cain was the heart of the group was a good one, because he was, but not at first. Because then Glitch would have been the brains of the outfit, and Raw their most courageous member, and they weren’t, just the opposite.
They gained what they’d lost (or had taken, rather) as they progressed on the journey, so that Cain gets his heart back by learning to love/be loved by his companions, Glitch gets his brains back (albeit briefly), and Raw finds courage while defending Glitch and Cain and the little Viewer from stick-wielding madmen in the control room. (If this theory holds up it means Raw was once very brave, as Glitch was once very smart, and so too then Cain must have been very loving in the Adora days.)
All three had traumas that changed who they were on a most fundamental level, the genius lost his marbles, the loving family man became bitter, hard, and vengeful, and the (presumably) brave viewer became timid and afraid. (though we never found out why)
Cain’s seen as the protector of the group, and he was, but I don’t think that’s what bonded him to his companions. Simply leading and guarding them across the O.Z. could have just been seen as an extension of his job and still allowed him to keep them at arm’s length emotionally (which he did try to do at first). What really touched him was that all of his companions rescued HIM at one time or another - DG rushed down to release him from the suit, Raw healed him from a wound, and Glitch saved him from dying of cold – which I find most interesting as “cold” is also a metaphor for lack of emotion or heart.