Theory Time

[JJ Strife]

I thought he was freaking out because one of his bodyguards just got killed!

My current theory is that the Dominants go unconscious while they summon the Eikons, and so if the Eikon is killed, the Dominant dies too. So Joshua and his Phoenix will be killed by Ifrit near the beginning of the story, and the rest of the story will be a revenge quest by his "Shield" who failed to protect him.

Oh and the reason his mother (?) said he shouldn't be outdoors is because they were hiding the fact that he's the Dominant, so the enemy couldn't target him.