About the true ending of Bravely Default

I'm at the final chapter, fighting the penultimate boss. I'm having a hard time beating her.

I've been reading online, and from what I gather is a true and false ending.

Apparently, if you follow the story, awaken all the crystals several times, and beat the boss, you will fight the ultimate real boss and get the true ending.

If you destroy a crystal, uh, the battle with the penultimate boss will be easier? I don't quite get it:

• What exactly happens when you destroy a crystal? Do I not get to fight the ultimate real boss?
• Can you destroy a crystal before the final chapter?
• If I get the false ending, can I get the true one later? And viceversa.

Solution 1:

If you destroy a crystal, you do not get to fight the real ultimate boss, nor the final form of the penultimate boss.

You can destroy a crystal as early as Chapter 5. You do not have to wait until Chapter 8.

If you get the false ending, saving your game after the ending and loading it will put you back before you destroyed the crystal, so you can then proceed to get the true one later. Getting the true ending will put you back on the final chapter with all four crystals not yet awakened so you can then proceed to get the false one later (and this also makes Genome Abilities related to the crystal bosses always obtainable).