Aeon. Or Fiend?

[Roogle]

Anima can be summoned by the Guado summoners

when did that happen?

I thought that the Dark Aeons were summoned by Guado Summoners to stop your party at various points of the game. This sidequest is not available in the North American version of the game. Can someone confirm this for us?

Indeed. Isn't Lady Yunalesca responsible for turning Guardians into the Final Aeon? Her defeat seems to be the act that makes the Final Aeon stop being an option for Yuna's party.

Yes. Yunalesca was the only one in Spira to know how to create a Final Aeon, so her defeat effectively ends the cycle of death and tradition that had persisted in Spira for ages.