You need to have 100% completion. Another things that you must have is that before the final battle, you should have got all the 44 lorestones. The game has 11 sequences. You can keep track of your lorestone progress as you finish the game using the lorestones. You will see a circle of red runes, each set separated by a dot when approaching a lorestone. The dot signifies divisions of the chapter. When you collect a lorestone, you will notice that the circle of red runes have turned white. When a section between the dots has all white runes and no red runes, it means you have found all the runes in that sequence. Find all the lorestones and see the super cool extra scene before the final boss battle.