The reason I find Kairos to be involved - is due to a couple of oddities. 1 of which is writing related the other is involving the character.
I find it EXTREMELY odd to introduce something of that nature (Kairos) for it not to show up again. IN FACT. It was interesting that in the MSQ, for the accident, Emet did not exactly objecte to being at Kitisis. So I feel this was part of the tour and it wasn't just to talk to Hermes, they were very likely to have gone to seen said device and likely knew about it. If Elidibus at that time was head - makes sense that he would have likely mentioned it and tasked Emet to go see Hermes.
https://youtu.be/FnaqXPQ3WCU?t=1283
In reference to the paradox if Hermes would have recognized the WoL: Themis doesn't need to have the WoL present. Simply, ask for a range (specific time) to be erased. It hasn't been addressed as to why Elidbus would 1. Had an erasure of memories to begin with when Venat apparently does not. 2. Be stubborn about looking at his own memory crystal despite the insistence from Emet. So I wouldn't be surprised of the story has something to address that disparity for the hosts/cores of Zodiark and Hydaelyn.