Partially driven mad by suffering, Nagumo Hajime (Arifureta Sekai Saikyou) has abandoned most of his compassion and mercy, killing all his enemies in cold blood.
Akame (Akame Ga Kill!) has been conditioned to be a near-emotionless assassin who is notorious for killing her targets in cold blood.
Kurome (Akame Ga Kill!) has been conditioned to be a near-emotionless assassin who is notorious for killing her targets in cold blood.
Kazuo Kiriyama (Battle Royale) is completely emotionless due to brain damage, allowing him to operate at full efficiency in everything, and is considered a demon of emptiness.
Once known for his heartlessness during his time as an Eraser for Chronos, Train Heartnet (Black Cat) would kill his targets efficiently and mercilessly.
The Executive Militia (Bleach) of the Onmitsukidō are known for their cold-bloodedness to execute traitors.
Ulquiorra Cifer (Bleach) represented the nihilistic aspect of death, and as such, showed no emotions.
Tokinada Tsunayashiro (Bleach) was a complete apathic sociopath, due to reading the Original Sin committed by his ancestors corrupting his sense of morality.
With eyes like that of a reaper, Rei Ōgami (Code:Breaker) can kill anyone he deems evil in cold blood, ignoring all pleas and reasons.
Yukihina (Code:Breaker) remains stoic whether expressing to avenge his friend's death, slicing through Houkabe's hostage, or blowing a pleading Houkabe apart.
LuluBell (D.Gray-man) is the only Noah who doesn't show emotions or caring at all, mercilessly killing Akuma's if failed to do the task. The only time she ever showed emotions when witnessing Mimi's death.
Hei (Darker than Black) became a Contractor when his sister fused with him, thus (mostly) acting on rationality and logic while not letting emotions get in his way.
Luc (Darker than Black) is typical for a Contractor, being aloof and indifferent even when his partner Kenneth insulted him.
Wei Zhijun (Darker than Black) is a Contractor, thus acting on rationality and logic while discarding his emotions. However, he developed an obsessive grudge against Hei, which was unnatural for Contractors.
Harvest (Darker than Black) is a Contractor, thus acting on rationality and logic while discarding his emotions. However, he developed an obsessive grudge against Hei, which was unnatural for Contractors.
Tanya Akulova (Darker than Black) is a Contractor, thus acting on rationality and logic while discarding her emotions. Such that she easily killed her boyfriend when he would not give up on her.
As a doll, Yin (Darker than Black) has no emotions, however, Yin displayed emotions and her own will. Although emotionless she possesses a deep connection to Hei to the point of falling in love with him.
Showing the typical apathetic trait of Saiyans, Vegeta (Dragon Ball Z) easily dispose of Nappa for losing his ability to fight despite their longtime comradeship.
Broly (Dragon Ball series) crushing his father and his space pod for trying to abandon him on a dying planet, showing a cruel disregard for even a parent who raised him.
Although Ryuk (Death Note) may seem sociable and at times vulnerable to easy mind games, in the end he is a still Shinigami, uncaring for humanity, as he coldly killed Light Yagami once he saw the man has nothing more to offer him.
Mard Geer Tartarus (Fairy Tail) has long since suppressed his own emotions and believed that emotions are a hindrance.
Euclid Lucifuge (Highschool DxD) became immensely nihilistic and apathetic after his sister betrayed their master Lucifer, to the point he can destroy countless innocent lives without a single shred of remorse.
Kanna (InuYasha) is a demon of the void and has no emotions as a result.
Learning to deny her emotions during her intense training, Chimera (Marchen Awakens Romance) is amongst the most silent and mysterious Chess Pieces.
Loco (Marchen Awakens Romance) suffered an unknown tragedy in her past which broke her spirit. As a result, her eyes and voice alike display no emotion.
As a creature created from collected evil energy, Orb (Marchen Awakens Romance) never shows any emotion or humanity aside from the malevolent thoughts of the souls that created him.
Due a lack of parental love, Sasori (Naruto) grow into an apathetic and cold man, his puppet body is a physical metaphor of an empty and emotionless vessel.
Sai (Naruto) has gone through Root's extensive mental condition and training, resulting in him being almost completely emotionless, until spending time with Team 7 and Naruto Uzumaki.
Sasuke Uchiha (Naruto) cruelly and apathetically piercing through his comrade Karin to kill Danzō Shimura in order to avenge his brother, Itachi's sufferings.
Obito Uchiha (Naruto) shows no sympathy for anyone due to his hatred of reality, causing the death of his mentor and violently attacking his former comrade and friend, Kakashi Hatake.
Kisame Hoshigaki (Naruto) is like many Blood Mist era Kirigakure ninjas, being conditioned to abandon their emotional attachments by killing comrades, something Kisame is all so willing to do.
Madara Uchiha (Naruto) cruelly and apathetically stabs his fellow-clansman, Sasuke, for the sake of his own Eye of the Moon Plan/Project Tsuki no Me.
Unlike his colleagues, the Sound Four, Kimimaro (Naruto) very rarely showed any emotion.
After massacring his entire clan, Itachi Uchiha (Naruto) hid away his pain, feelings, and secrets for the sake of protecting his brother, Sasuke.
Kushimaru Kuriarare (Naruto) is one of the "Heartless Pair", having committed many cruel acts that included killing his own teacher...
Jinpachi Munashi being the other one, having killed his own brother among other cruel acts.
Indra Otsutsuki (Naruto) was Hagaromo's eldest son, who despite being incredibly gifted in every known jutsu lacked the compassion his sibling inherited.
Deepa (Boruto) is an apathetic sociopath, remorselessly killing civilians after eating in a restaurant simply to keep his own identity elusive, in that even his comrades neither trust nor understand him.
When Bartholomew Kuma (One Piece) became a living weapon, he lost his free will and became a heartless "human weapon".
The Vinsmoke Brothers (One Piece) were genetically modified to have their emotions completely removed to the point they are apathetic even towards their own deaths.
When Shinichi Izumi (Parasyte) had his cells fused with Migi to repair his heart and before the death of Reiko Tamura, he became distant, unsympathetic, and lost the ability to empathize with others, as he not only thinks but feels emotionless like a parasite.
Seta Sōjirō (Rurouni Kenshin) giving his trademark false smile, hiding his emotions and rendering him unreadable.
Yūkyūzan Anji's (Rurouni Kenshin) tragic past led him to become apathetically ruthless towards evil such as the village chief, ignoring the man's pleas for mercy as he crushed his head.
Shinomori Aoshi (Rurouni Kenshin) discarded his emotions when his four comrades died saving him, in his path to gain the title of the strongest.
Gowther (The Seven Deadly Sins) lost all his memories, feelings, and entire sense of self after he removed his artificial heart.
After her dream demon was killed, Yumi (Yumekui Merry) lost all her hopes and dreams, leaving her an apathetic and emotionless shell.
Because of his empty mind, Strings (Yu-Gi-Oh!) is unable to display any emotions.
Having been experimented on and abused for most of his life, Dufort (Zatch Bell!) rarely displays emotion for the world he has come to hate.
Believing his destiny is to cause absolute destruction, Clear Note (Zatch Bell!) can do sadistic and evil actions in a calm and near-emotionless manner.
Bi Ki, the Queen Mother of Qin (Kingdom)
After killing her little sister in the Shiyuu ritual, Yuu Ren (Kingdom) completely severed any emotional attachments to finalize her training as a full-fledged assassin of Clan Shiyuu but slowly went insane as a full result.
When she was human, Hida Nayuta (Hybrid × Heart Magias Academy Ataraxia) lacked any human emotions, feeling nothing for all forms of life. Even her own children meant nothing to her when they had no more uses for her.
A quiet man, Golgo 13/Duke Togo (Golgo 13) shows no remorse toward his targets as he coldly kills anyone who gets in his way.
Johan Liebert (Monster) often shows complete apathy for life, he is able to use others without any remorse.
Kyubey (Puella Magi Madoka Magica)
After shattering his heart to seal the Raven away, Mytho (Princess Tutu) lost his ability to feel emotion.
A solid man, Woo Jin-Chul (Solo Leveling) rarely shows any emotional expressions.
As a skilled assassin, Killua Zoldyck (Hunter x Hunter) can suppress his emotions to focus on killing his enemies.