Burner is a spirit that inhabits Daniel Ferris's wakizashi, and is presumed to be the source of the sword's supernatural powers. It appears as a large humanoid, that is constantly out of focus, except for its glowing red eyes, which can always be seen in unbelievable detail. Daniel is the only one able to see it, and only if it wants to be seen. Neither Daniel or Burner know anything about its past, but its implied that The Blind Man may know.
Daniel was briefly brought inside of Burner, and perceives a world with an endless metal ground, coated in several inches of water, a plain white sky, and large Japanese sword blades protruding from the ground into the sky, like massive skyscrapers. Another being, which Daniel calls Flicker, also seems to inhabit this world.