This Epilogue is locked for all users until they complete they campaign in Aurora. 

In order to fully unlock "The Call of the Babel" you need to meet the following conditions other wise it will remain locked. 

Captain Vettel,Chloe,Victor,and Neica must be alive until end game! If any of them died well sucks to be you. 

Neica, Chloe and Victor must be promoted before end game. 

You must get Chloe,Victor, and Vettel personally weapons. 

Any other units counts as bonus that will affect the Epilogue later on. 

Difficulty: Realism only! 

The Story will start depending on what ending you got during your Aurora Campaign.