Shishkebab

Shiskebabs are melee weapons that can be obtained in Fallout 3, Fallout: New Vegas, and Fallout 4.

Shishkebab
Shishkebabs are makeshift flaming swords built from assorted materials scavenged across the wastes. The blades consist of a lawn mower blade affixed to a shower guard, with a motorcycle brake and a pilot light used to manually ignite the blade. These contraptions are connected via a hose to a motorcycle fuel tank, worn on a surplus frame upon the back. To prevent burns, shishkebabs are handled with oven mitts.
 * For the unique Shiskebab that was added in the add-on Gun Runners' Arsenal, see Gehenna.

Wakizashi Shishkebab
This particular Shishkebab is a Finch family heirloom, created by the grandfather of Abraham Finch out of a ceremonial Japanese blade (a wakizashi) salvaged from a museum. He welded a Schoelt propane tank to the handguard, connecting it to a series of nozzles mounted along the surface of the blade, adding a small pilot light and control lever to effectively control the flames. Although decidedly unsafe, the resulting contraption was far more lethal to his foes than to himself and he went on to establish a family. Unfortunately, his great-grandson, Jake Finch, turned out to have little reverence for history or ancestors and stole the Shishkebab in a poorly-thought-out bid to ingratiate himself with the Forged and Slag when they seized Saugus Ironworks.

Behind the scenes
As discovered through concept art for the weapon, it was originally referred to as the "shishkesword," and would have used a flattened crowbar for a blade instead of a lawn mower blade.