>>281610164
>>281610200
The way I understood it, is that the summons are instances of the same mind that resynchronize when they are not summoned. Almost like a hivemind AI where the individual summons are just copies of the original mind that is updated with each summoning.
And so far there is only one Merus, who willingly signed up for the job. So he's probably unique in that regard unless something changes with S rank summons.