Quote Originally Posted by blackmage_nuke View Post
(SPOILER)Being from zanarkand, jecht as sin has the ability to travel between spira and dream zanarkand (for reasons i cant remember but theyre there)

Auron rides jecht to get there. It might help that he's unsent but im not sure
(SPOILER)Jecht being from DZ has nothing to do with it, other than a possible greater chance of going to DZ than otherwise, since Jecht likes to see Tidus. Its simply because DZ is located out on the sea somewhere, and Sin, any incarnation of Sin, can travel to DZ. Auron, like Jecht and Tidus, can ride Sin to and from DZ provided Sin is headingto and from DZ. When Braska defeated Sin with Jecht, Jecht became Sin, and Auron, after his death, hitched a ride to DZ to watch over Tidus as per Jecht's request.

The technical explanation is that because Sin is made of pyreflies bound using gravitational magic to it, it can temporarily bind any entity made of pyreflies, such as the Unsent Auron and the aeon's Tidus and Jecht. This is why they can ride Sin. It also explains "Sin's Toxin" in normal folk, but that's another topic entirely.