Freedom isn't what Tiamat needs. Get that dragon some therapy! Are there any dragon psychologists available? I think the poor girl is in serious need of some grief counseling. She may be putting a bit too much of the burden of blame on herself, as well; I'd say the Ascians and Allagans had a FAR greater stake in the disaster than she herself did. I'm guessing she understands that, logically, but emotions can be a bit more tricky... So, counseling!
Seriously, though, as easy as it would be to make Tiamat a permanent fixture in Azys Lla, seeing Tiamat recover from her grief is one of my greatest wishes for the game.
Yeah, bear in mind that the Allagans did their thing more than five thousand years ago during the Third Astral Era. All the drama with the Ishgardians, Ratatoskr, and Nidhogg happened less than a thousand years ago, during the Sixth Astral Era. That's quite a difference in timespan, and Middy could easily have felt that Niddy was well within his rights to still hold a grudge, even while feeling that Tia might be a bit of a drama queen about the whole Bahamut disaster.
