This Achievement is for "inheriting" Steady Hand McDuff's equipment. McDuff is a blacksmith located in the Lost Bastille. To reach him, start from the first bonfire you come across in the Bastille after leaving No Man's Wharf. Go down to the lower level and follow the path until. You should come across a closed gate that needs to be opened with a switch, and a set of stairs shortly after that. McDuff can be found in a room just to the side of those stairs, but it takes another step to reach him.
If you look up the stairs, you'll notice one of those giant mummies standing just behind a powder keg. You need to go up the stairs and push the powder keg down back down the way you came, so it hits the wall at the bottom. This will open a hole in the wall, thereby giving you access to a new bonfire. McDuff is in the room right next to this, sitting on top of a treasure chest. You'll want to light a torch at the bonfire and use it to light the brazier in McDuff's room. Warp away from here and come back, and he'll have moved off of the chest and gone back to work at his anvil.
Your work is only just beginning, though. In order to get McDuff to work on your equipment, you need to find the Dull Ember. This is found in the Iron Keep. From the first bonfire in the keep, just follow the path until you get to the open outer area with what appears to be a very large furnace in the middle. Lower the bridge with the nearby lever, then cross over to the other side. Take a right once you get there, then line yourself up so you can jump across to the nearby platform. The ember is on a corpse right at the edge here.
Now with the ember in your possession, you can head back to McDuff. Hand it over to him and he'll offer to upgrade your equipment. To earn the Achievement, you must spend at least 50,000 souls at his shop, with at least 10,000 going towards infusing weapons. Take any five weapons you like and infuse them with whatever stones you have available (fire, lightning, magic, bleed, etc). Just make sure to use a different type of stone for each weapon, or else the Achievement won't pop. Now speak to McDuff again using the "Talk" option and he'll give you a free titante slab. Achievement unlocked!
If for whatever reason you don't have five stones on hand, Stone Trader Chloanne will begin selling them at her spot in Majula towards the end of the game.
There appear to be a lot of conflicting reports on how to unlock this one. At the very least, this solution can be used as a guide for anyone who doesn't know how to locate McDuff and / or the Dull Ember. I'll update it again once the exact requirements for the Titanite Slab have been figured out.
User KetchupKleenex has added that this might require you to spend 14k souls on upgrades in order to get this to work. Souls spent in his shop do not appear to count towards this total.