I Thrust at Thee
Perhaps the easiest way to earn the achievement is to play the Flood gametype. Although the Flood's melee appendage functions nearly identically to the Energy Sword, Flood kills award a Melee medal rather than a Sword Kill medal, and therefore will unlock the achievement. Additionally, the thruster pack is one of the default Flood loadouts in the gametype. Perhaps the most difficult part is simply having a Majestic map selected in matchmaking, which will require all players to have downloaded the Majestic Map Pack.
The achievement's name is play on a quote from the novel Moby-Dick. After stabbing his nemesis, the eponymous whale, with a harpoon, Captain Ahab yells, "...from hell's heart, I stab at thee!" He is then dragged underwater by the whale and drowns with it. The first part of the quote was referenced in the Halo: Reach achievement From Hell's Heart.