Spoilerfree solution, do not read the comments if you want to keep it that way, someone decided to spoil it in there.
During the Companions' questline, 'The Silver Hand' to be exact, you will be given the choice of joining the Circle.
Accept their gift to gain a new power along with this achievement. This new power has pros and cons, so you might want to check a wiki and reload the game if it doesn't suit you.
The Companions are located in the Jorrvaskr house in Whiterun and can be joined at any point throughout the game.
Credit to: Fatal RusH