According to Bobby Singer, the Buruburu are ghosts born of a person's fear after dying in a terrifying manner. They can then infect others with their fear, and this infection is known as the Ghost Sickness. The people they infect are usually people who have made a habit of terrorizing others. Because it is a type of Ghost, it has all the same abilities and weaknesses as a ghost, but it differs in one notable way: it can be "scared to rest." It is a spirit form first categorized and documented by the Japanese in the Edo period, and the book that Bobby had on the subject was in Japanese.
Dean was infected with the ghost sickness, and Bobby and Sam deduced that the culprit was a Buruburu born from the terrifying nature of Luther Garland's death. Luther was chained to a truck and dragged up and down a gravel road until he died, so it was impossible to find and burn all of his remains. The victims of Luther's ghost sickness had all died of heart attacks brought on by crippling fear, so they had to find another solution quickly.
Finally, Sam captured the buruburu with an iron chain etched with spell work and then had Bobby drag his ghost down the same gravel road where he died, re-enacting his death and literally "scaring him to rest." This happened not a moment too soon, as Dean was having hallucinations of Lilith and was close to having a heart attack of his own when they finally managed to defeat Luther's spirit. 
Powers and AbilitiesEdit
A buruburu has the standard powers and abilities of a ghost and some unique abilities:
- Ghost Sickness - These ghosts are able to cause ghost sickness, a flu like illness which results in growing fear, panic and anxiety, enough to cause hallucinations and a fatal heart-attack.
- Teleportation - Buruburu can vanish and appear instantly across a building.
- Electrokinesis - Luther Garland could manipulate the machinery at the saw-mill he haunted.
- Super Strength - As seen with most ghosts, Buruburu can easily overpower humans, with Luther Garland being able to overpower Sam until he was bound with iron chains and dragged by a car.
- Salting and Burning the Remains - Placing salt on and then burning the remains of a Buruburu causes their ghost form to burst into flames, permanently dispersing them.
- Salt - Like all spirits, Buruburu are unable to pass through salt and can be dissipated though contact with rock salt.
- Iron - Buruburu are unable to pass through iron, which can be used to dissipate them on contact. An iron chain which branded by (possibly) Japanese sigils or spell works is capable of binding them effectively.
- Scared to Rest - By repeating the method in which they were originally killed, they can be scared into rest.