So why they didnt take the seraphins after devon touch saturn? They left the seraphins in egg head...
Devon's mission seemed like a pretty covert operation, maybe they weren't prepared for transporting them all, or thought it would be too risky to try and nab all the seraphim when there's an entire navy fleet, and the actual Saturn, occupying the island. It won't be too hard now to nab them the next time they're deployed. No need for unnecessary risks.
Seraphims ain't dumb fucks though.
It really isn't Saturn himself. There must be some Bio-metric used for it.
Depends on how good Devon's shapeshifting is, I guess.
It can't be anything about fooling the WG or infiltrating Mariejois, though, since Imu and the gorosei know Saturn's six feet under (and would try to murder him if he wasn't.)