Fiorin would perceive it as an itch in the back of his mind. He will feel it, but may not know its significance. The more he is around other Immortalis, the more the skill will develop. Eventually, it is one that every Immortalis gets. The Elders are pros at this, but for the Childer Immortalis, it will take time to cultivate.
Fiorin is an Immortalis, but has not technically sided with the Ageless or Forsaken at this point. I'm sure you've already read up on this but just for the purpose of summary:
Ageless: When not assisting in the human realm, the Ageless reside in the capital city of Avalon, a place that can only be reached through a "Gateway." The Ageless are dedicated to the preservation of humankind and serve a benevolent being known as the Divine. The leaders of the Ageless are the Archon (Oran Raven) and the Blood-Warden General (Deya Fury.) Together, they lead The Bulwark of Heaven, the strongest of the Ageless who generally do battle on the frontlines. The majority of the Ageless end up joining the Bulwark at some point in their existence.
Forsaken: Are dedicated to the destruction of humanity and when not terrorizing, raping, pillaging and plundering, reside in their capital, Darastae, which is a horrific reflection of Avalon itself. Their leader is Severan Deceit (once known as Severan Victor.) He was once an Ageless who defected and became the champion of the Adversary. Severan is exceptionally powerful, but generally tends to avoid the frontlines. His second is Lt. Cauter, who loves nothing more than capturing and torturing Ageless, and slaughtering humans.
You technically have a choice in which faction you want to join, but right now, you are in the company of an Ageless party. Everyone will have the opportunity to defect to the Forsaken should they choose to, knowing it will likely put you at odds with other PCs.