Defeated the Nemesis.
You will fight the Nemesis in chapter 9.
This can be quite a long and frustrating battle. Make sure you keep your distance and dodge whenever it charges you because you WILL die if it hits you. Keep using power throw to slow it down. After a while, it will charge its blade with electricity and then throw it at you. If you can, dodge it. Now charge your glaive by throwing it at the Nemesis' blade, which will be lying on the floor somewhere. Throw your glaive at the Nemesis to take down its shield. Two hits will destroy its shield and one more hit will stun it. Run up and press B to engage a little button-mashing sequence.
Complete this process a total of 3 times to defeat the Nemesis and unlock the achievement.