This achievement is for defeating the last boss in the game and cannot be missed.
This is the same as the similarly named achievement from the original 360 version.
Here is the original solution from Onsidic.
Final Boss fight.
Phase 1 - Dragon Stage
Phase 1 a -
Another cutscene follow and onto phase 2.
Phase 2 - Human Form.
Watch the cutscene, and earn your achievement.
Then watch the credits if you really want to.