The Reaper

God of Death (GoD) is the world's best assassin.

It is later revealed that he is not the original God of Death and was in fact his disciple.

Appearance
Contradictory to his name, the GoD has a somewhat innocent looking and friendly smile. While disguised, he has short hair and is always seen with his cap. In truth, he has a skinless, skull-like face after intentionally ripping off his own face.

Personality
As the world's best assassin, the GoD is a sadistic person. He has said terrifying things such as dividing Irina Jelavic into pieces, and drowning Korosensei along with all of Class 3-E. On the other hand, he is quite arrogant and egoistical (which proved to be his own downfall).

History
The GoD was born in an extremely wealthy family. One night, his father was killed by an assassin. As the God of Death saw his father's assassination from a window, he admired the assassination. Calling it "A beautiful skill", this motivated him to become an assassin. In Chapter 134, it was revealed that he was originally Korosensei's disciple (who was the GoD at the time) right after Korosensei had finished the job of assassinating his father. Korosensei trained him until the latter betrayed him during an assassination mission. He stole Korosensei's title of the "God of Death" with the result being Korosensei's capture.

Plot
He is first mentioned by Lovro when Nagisa asks about the world's best assassin. He appeared to Class 3-E in the disguise of a florist in order to sell them some flowers, which they would later give to Karasuma to give to Irina Jelavic. He had planted a bug in the flowers to gain Intel on Irina before moving in to kidnap her. After Korosensei left for Brazil, he took the opportunity where there were no teachers available to approach the students. He showed them a picture of Irina in captivity, stating that if they didn't rescue her he would dismember her, and send her back to school piece by piece. This was also where he displayed his inhuman powers, such as natural blending in with the classroom to appear invisible as well as disappearing silently without a trace after throwing some petals in the air.

Abilities and Powers
At first glance he doesn't seem to be very wicked, but this is one of his best skills and assets: the power to appear as a harmless individual. Upon his first appearance, he appeared before Lovro undetected and had him comatose with ease. He was responsible for the decrease in assassins after solely defeating them all himself. He is so powerful that rumours persist that he is actually ten people as opposed to a single one, and instances in the manga imply him to be almost supernatural in power.

One skill unique to him is his control of his bloodlust. He can either hiding it completely along with his presence to "blend" into the background, or release so much that it transforms into a "shroud of darkness". This latter trait blocks visual perception of his body with the only perceivable form being that of an approaching shadow.

He has demonstrated being a powerful and intellectual planner, easily trapping the entire Class E and even Korosensei while compensating for most miscalculations. He was technologically savvy enough that in the place of accomplices, he's able to solely perform multi-person tasks; using a remote to operate certain contraptions around his entrapped hostages, and control doors and bars.

Deceptively he is an extremely powerful hand-to-hand combatant, an unusual trait amongst assassins that is useless in the field 99% of the time. However the other 1% of the time, it is fundamental should an assassin ever find himself in such a fight. The GoD was masterful enough that he could defeat almost every hand-to-hand specialist, including Nagisa, in Class E.

Another of his powerful skills is his marksmanship. He is able to attack targets at long-range while in motion, best exemplified by his sniping of a target who was sitting inside a bypassing train. His shot was so precise that he completely hit all of Korosensei's tentacles as he tried to grab hold of the floor despite their intense speed. This demonstrates his impressive eye-sight as with this skill alone he overwhelmed and trapped Korosensei.

Trivia

 * His technique of becoming a shadow-like being to commit assassinations is similar to some accounts of death where people report shadow people encroaching towards them as they die.
 * Instances in the manga resemble him as either as flower, a skull, or simply a shadow.
 * When described by Lovro, the image used in the manga resembled a man holding a book.

Quotes

 * (To Class E students) "It's impossible for humans to reap the God of Death. Do not fear, there is only the God of Death reaping man."