Akame (Akame Ga Kill!) is a deadly assassin with her skills and equally deadly Muramasa sword.
Kurome (Akame Ga Kill!) is a deadly assassin, with drugs and experiments inserted into her body and her dead-controlling sword, Yatsufusa.
Korosensei (Assassination Classroom) is a master assassin, once known as the God of Death.
Nagisa Shiota (Assassination Classroom) is a professional assassin, able to taking down a special corps soldier with years of experience in less than a second, while coming from in-front of him.
Sosuke Aizen (Bleach) assassinated all the members of Central 46.
As the Commander-in-Chief of the Onmitsukidō, Suì-Fēng (Bleach) is one of the foremost masters in the art of assassination.
Both Urahara Kisuke and Shihōin Yoruichi (Bleach) were formerly in the Onmitsukidō, as Yoruichi was the former commander in cheif, and Urahara her lieutenant, and are masterful assassins.
Haruto (Code:Breaker) is a very powerful assassin even before acquiring his powers, having a success rate of 99.9%.
Tao Pai Pai (Dragon Ball) is such as skilled assassin that he can kill people using only his tongue...
...and after becoming a cyborg, Tao has eschewed the honor of a martial artist to truly devote his efforts to kill his targets at all cost.
The members of Trinity Raven (Fairy Tail) are the strongest of the Assassins in the Death's Head Caucus guild.
Jacob Lessio (Fairy Tail) is a genuine master of Magical Assassination, and one of the Spriggan 12 which makes him all the more dangerous.
Nobume Imai (Gintama) is a master swordswoman and the commander of the Mimawarigumi's assassination unit.
Mukuro, later Nobume Imai (Gintama) has been trained by Tenshoin Naraku as an assassin from child, and her skills is such that she is one of the Three Wings of Naraku, and is called the "Bastard Child of the Death God".
Oboro (Gintama) the leader of the Tenshoin Naraku, considered to be the strongest assassin within group, with his mastery of Hakkei and acupuncture needles to back up his reputation.
The Zoldyck Family (Hunter X Hunter) are the top assassin group in the known world.
Killua Zolodyck (Hunter X Hunter) can use techniques to assassinate.
Kakashi Hatake (Naruto) was once an assassin working as an ANBU.
Momochi Zabuza (Naruto) was one of the most infamous assassins of the Kirigakure, as his Silent Killing, especially combined with Hiding in the Mist technique, is second to none.
Kisame Hoshigaki (Naruto) was an assassin of the Kirigakure, and would kill even his own comrades to protect what he deems important.
Sai (Naruto) was an assassin for the Root organization, going as far as to eliminate emotions, and was said to be the strongest of his generation.
Nico Robin (One Piece) is skilled assassin.
Rob Lucci (One Piece) was the strongest of the CP9, the World Government's secret assassination squad, even at the tender age of 13.
Jabra (One Piece) is the third strongest assassin of CP9, though he kills more than he needs to.
Shuzen Akua (Rosario + Vampire) is the assassin of the Fairy Tales, and formerly of the Miao Family.
Golden Darkness (To Love-Ru) is a legendary intergalactic assassin.
Younger Toguro (Yu Yu Hakusho) has been hired by many as an assassin due to his fame.
Elder Toguro (Yu Yu Hakusho) is hired by many as an assassin due to his fame.
Kyou Kai (Kingdom) is a descendant of legendary assassins known as the Shiyuu, a clan infamous for their bizarre and unique ways of killing.
Out of all the Trinity Seven, Levi Kazama (Trinity Seven) has killed most during her assassination missions, and achieved perfect success rate in both missions and assassinations.
Sham Lash (Magi The Labyrinth of Magic) the Parthevian Empire secret assassination squad.
As the leader of the Sham Lash, Shaka (Magi The Labyrinth of Magic) is dangerous master assassin, able to massacre countless people by himself...
...and kill a Household Vessel Assimilated Giant Monster with a single ki infused attack.
Jafar (Magi The Labyrinth of Magic) is a child prodigy in assasination, having once been one of Sham Lash's most elite assassins at 10 years old.