This Astral Chain Zeus Boss Guide will teach you how to successfully go through the first boss encounter in File 05 of the game.
Astral Chain Zeus Boss Fight
The Zeus is a big orange frog with a mutated face, a long tongue, and similar-looking smaller minions.
The minions do not require much effort to put down and most of the work is to be done on Zeus. Although he looks more menacing, Zeus is not a tough boss on his own.
Using your Arm, the minions could be easily defeated. I would personally recommend the Hit Rush attack, it would let a legion deal with the smaller guys while you can use the other one to work your way around Zeus.
Wrapping up the enemies with your legion leaves them stunned and lands you the opportunity to deal more damage using the Arm Legion.
The dazed man needs to be escorted off once you are done dealing with the hoard of enemies. The escorting point is just a short trip away.
While escorting the man you would come across some other enemies that would have to be dealt with.
You can use the legion here to help you out or even put down the civilian if you want to fight more freely. A personal recommendation here would be the Hit Rush attack again.
After completing this, answer the call from Alicia and follow the waypoint to her. There would be more enemies you would have to face on the way. Defeat them and move up the escalator to proceed to the main boss fight of the mission against Deimos.