Grim Reaper

Grim Reapers, due to their prominent place in human culture, are frequently imagined as personified forces. Reapers are beings that serve Death. They assist in maintaining The Natural Order and used to be thought as completely neutral, aligned with neither Heaven nor Hell nor Purgatory, deciding to remain in the Demon Realm for numerous purposes, residing in the Phantom Territory, a territory who was destroyed 300 years prior to the events of the series.

Characteristics
Reapers are required for death to occur. They wait until a person meets the end of his or her life (either through accident, or simply the natural end point of that person's life) and then touch the person causing them to die, they then escort their souls to Heaven or Hell. They do not however possess the power to force souls to go with them. It's unknown if they are required for death to occur to all beings or simply humans.

Reapers are completely neutral beings, not caring for deals, fate or even each other at times, all they care about is maintaining the "Natural Order" of life and death. Although sometimes uncaring, Reapers generally sympathize with their victims, but refuse to make allowances, regardless of who or why. As they can't force anyone to go with them, Reapers must convince the souls to leave with them, which they normally achieve by forewarning the fate of the souls if they refuse they will be transformed into ghosts and trapped on Earth forever.

Reapers are also impartial in other ways, and rarely interfere in any manner other than performing their duties, and although they have the power to, they do not kill people before their time. However, there is one possible account of a Reaper ignoring the Natural Order, when that one Reaper who had been bound was freed, he quickly turned on and killed the person who bound him. This is the only known occasion of any Reaper ever being the cause of a person's death. As the person in question had forced the Reaper to go against the natural order by taking those in the place of others whose times were up, this can be an exception.

Some Reapers do break these trends however, leading to rogue Reapers. Unlike normal Reapers, these Reapers ferry souls out of their afterlives and take them to a different one, for the purpose of profit, and usually work for higher beings. They also ferry living mortals and at least one still ferried souls, at least those of ghosts put to rest, but on at least one occasion took a soul to the wrong place on his boss' orders.

Despite appearing stoic at times, Reapers are apparently as capable at experiencing emotions as humans, as on many occasions Reapers have shown sorrow, annoyance, compassion and anger. They also appear to have free will, although they rarely act upon it.

It is implied Reapers have a similar opinion of Death as angels do with God. It is unknown how they came into existence. Upon Death's release, hundreds if not thousands of Reapers flocked to meet, and receive orders from him.

It seems the Reapers have no sole shape, as some of them appear as ghost-like beings, beautiful women or elder men in mortician wear or suits. Commonly though, they appear as elder men in mortician wear, often black. Despite this they do have genders.

Reapers are able to possess humans. This may be how a few are shown to be able to manifest physically for humans to see them rather than being invisible to all but ghosts.

One of the laws of the universe is that after one incarnation of Death dies, the next Reaper to die will be promoted to take Death's place.

Powers and Abilities
As servants of the Horseman Death himself, Reapers are quite powerful and have extensive abilities.
 * Invisibility - Reapers can become invisible to the physical universe and can only be seen if they are dealing with the deceased or if they choose to. Spiritual beings, like angels, demons and deceased humans can see them.
 * Astral Perception - Reapers can see ghosts, angels and demons within the Veil.
 * Teleportation - Reapers can teleport from one place to another anywhere in the universe instantly. They can travel to any afterlife realm easily. It is also possible for them to take living humans with them, although it runs counter to their role in the natural order, and is therefore offered only by rogue reapers.
 * Dimensional Access - They can access Heaven, Hell, Purgatory and the Veil. Also they can take others with them as a spirit, a soul or even alive. However, they cannot enter spiritual realms if they have been closed.
 * Resurrection - Reapers can resurrect deceased humans, though their dedication to the natural order usually prevents them to.
 * Cosmic Awareness - Reapers have an incredible amount of knowledge of the universe, they know when a person is supposed to be born and die. They also understand many concepts, including the limits of power.
 * Chronokinesis - Reapers are able to stop time, causing objects that measure time to permanently break.
 * Astral Projection - Reapers can project their astral form.
 * Super Stamina - Reapers do not grow tired, and will nag their victims incessantly, unless a supernatural event disturbs them. However they do sometimes eat for pleasure.
 * Invulnerability - Reapers are highly resistant to pain and hard to kill. Higher beings, certain divine weapons and magic can be used to kill them.
 * Killing Touch - Reapers can kill humans by touching them.
 * Telekinesis - Reapers can move objects/beings with their minds.
 * Immortality - Reapers are not subjected to hunger, disease, or age.
 * Flight - In their true form, they can hover or levitate.
 * Perception Altering - Reapers can perceptually alter how humans perceive them, appearing in apparently anyway they want to be perceived. They do this to spirits to hide their more frightening form, enabling the reapers to communicate more effectively with their targets.
 * Disease/Death Transference - Reapers can use their powers to heal disease and injuries; however, they have to give the injury or disease to someone else.
 * Memory Manipulation - Reapers can make mortals forget things and can also restore memories.
 * Intangibility - In their true form or in vessels, reapers can pass through anything physical on Earth without any injury.
 * Electromagnetic Interference - The appearance of a Reaper can cause lights in a room to flicker or go out. A Reaper was also able to cause a car to lose power and stop.
 * Wind Manipulation - A reaper's arrival can cause sudden gusts of wind.
 * Biokinesis - Reapers can manipulate human biology; one angry Reaper once infected a person with a mental condition, giving them an early death in revenge.
 * Possession - Reapers can manifest on their own or use a vessel.
 * Banishing - Reapers are able to banish souls into the Empty, a place from where nothing can come back.
 * Soul Control - A Reaper displayed the ability to pull 200,000 souls from the Veil into a crystal as part of the Soul Bomb.

Weaknesses
Despite being quite powerful beings, Reapers do possess a few weaknesses:
 * Death - As their boss, Reapers were under Death's control.
 * Higher-tier Demons - Higher demons can overpower/possess Reapers.
 * Magic - By using magic, Reapers could be imprisoned, enslaved and killed.
 * Death's Scythe - It is capable of killing Reapers.
 * Reaper trap - A reaper trap will hold a Reaper, even two, in place and prevent them to escape and depowering them.
 * Angel Blades - Reapers can be killed by angel blades.
 * The First Blade - The First Blade is capable of killing Reapers.
 * Archangels - Archangels are able to destroy them easily.
 * Incinerating Spell - For unknown reasons this spell is capable of killing reapers.

Trivia

 * Reapers have started out being male but as the anime moved on, more female Reapers appear.