His father has to be involved in this humans-turning-into-titans business. There
has to be a link. We need to see him again, or that'll be a fail on the part of the mangaka.
I just finished the episode like over 15 mins ago and its still got me thinking!
EDIT: Ok, I have an idea about the armored titan and who it may be. I have to share.
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I think It's Reiner. They have the same hair. I know they were children when armored titan arrived that one time, but perhaps Reiner was able to control his power already by then. You know, because there is a secret to mastering the power,
and Eren hasn't figured it out yet, of course, which is the whole point of the expedition. I know he acted like it was a big surprise to see female titan when she attacked him, Armin and that other guy, but he could have just played pretend of course. They're
spies, they have to. Think about why Eren's father kept making trips outside those walls before the attack. Perhaps to train them, as he was attempting to train Eren.