While we are indulging in speculation, my personal pet theory for eiki is paranoid cop. Everyone is guilty.
Re: XIII:
Even though it's not concrete, I think XIII killed himself. Reading about the zombie role its basic function was to bite others. I wouldn't be surprised if it was some sort of mason role that recruits through infecting others, and that he targeted scum and was killed.
I don't think HGR took an existing role. I think HGR made something up based on the fact that the character is literally a zombie. It's a plot point that because she's a zombie, she regenerates rapidly and can come back from being beaten up -- based on that, I was thinking self-reviver.
I still have misgivings about how easily this day is going. Owl himself may have given up, but would a scumteam likewise be so quick to give him up when we're presumably very close to do or die?
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another place and time, without a great divide, and we could be flying deadly high