Complete the Game
Story related. Cannot be missed.
Will unlock in Chapter 30: Alecto's Chamber

After you reach Alecto's Chamber you will be thrown into the final boss battle of the game. In it you will fight the remaining Fury Sisters, Tisiphone and Alecto, in a multi-phase encounter on the ocean. Although it is the longest boss battle in the game it is arguably the easiest. If you are struggling with this fight on Hard difficulty, or would just like a complete walkthrough, please see this post for a detailed text strategy and video guide.

Once you have completed all 30 chapters of the game the trophy will unlock. It will unlock regardless of the difficulty you are playing on. The chapters, in the order you will complete them, are as follows:

Prison of the Damned
The Sewer
The Guard House
The Hecatonchires
The Village of Kirra
The Cistern
The Tower of Delphi
The Python's Belly
Ice Caverns
The Temple of Delphi
Delphi Catacombs
The Oracle's Chamber
Passage to Delphi
The Cistern (Part Two)
The Grotto
Prison of the Damned (Part Two)
Martyr's Chambers
Delos Landing
The Foot of Apollo
The Gauntlet of Apollo
The Forearm of Apollo
The Ribs of Apollo
The Furnace
The Shoulder of Apollo
The Furnace (Part Two)
Eyes of Apollo
The Lantern of Delos
The Trial of Archimedes
The Fury Citadel
Alecto's Chamber