Like a Dragon: Infinite Wealth

To keep this guide short, I'll only give some info on the bossfight that you'll face at the end of the sector: the shark that you already fought during Chapter 13, except even angrier-looking and level 60. The shark is resistant to ice, gun and electric attacks, so avoid using those. Instead, try to use as much blade and fire attacks as you can, since those are the weaknesses.

Once you've defeated the shark, watch the scenes until the achievement pops.