If you haven't finished the story, spoiler warning. Anyway, maybe...
[spoiler]Guardians are the darkness that killed the traveller. Ghosts everywhere are resurrecting all these guardians who have no knowledge of their past. Unknowingly, these guardians help the Traveller heal, only to have the Traveller turn on them. Plot twist! The Traveller becomes our ultimate enemy as we fight to survive the second collapse.[/spoiler]
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Heres my theory the darkness has framed the traveler as the darkness but this whole time it was the purple ball