[It's a surprise - though little can be relied on when it comes to Eren's memories right now.

But if he knows, it's irrelevant. He can do nothing with the information and their alliance has been solidified over the months.

Years, for some.

He's seen Loki. Robin Hood. Knows more than many.]

Yes. Though there's a stark difference between them, despite similarities. A persona is a manifestation of willpower and rebellion in a human heart. Robin Hood. Loki. Azathoth.

Shadows are the opposite of it, in a way. A suppressed, unwanted nature manifest to accompany distorted desires. Persona tend to be unique to the user. Shadows lack that. You can fight 'Pixie' multiple times. Narcissus, Barong, Garuda -

[Shido's palace. Shido's shadows.]

In clusters, over and over. They tend to vanish, and reappear.