In addition, there's the Hellhound, Guts's personal Heartless and Superpowered Evil Side, which was born from all the negative emotions that arose in Guts after the Eclipse went down, and which worked in concert with him during the Retribution/Conviction arc, but now works against him as his focus has turned to protecting Casca.
Qlippoth creatures, like ogres and trolls are also reflections of humanity's darkest side, being Astral Creatures. They are born through subconscious emotions, nightmares, and rumors/tall tales of their existence.
Bleach: When ghosts linger in the world too long, they become consumed by their emotions and transform into Hollows. Their hearts are transformed into masks that hide their faces, leaving holes in their chests, and they become creatures of base emotion and insatiable soul-hunger, driven to hunt and kill any humans with spiritual power. Powerful Hollows that lose their masks regain a part of their lost hearts and become capable of higher reasoning, becoming Arrancar. Hollows at higher stages of evolution (Gillian, Adjuchas and Vasto Lorde) usually hunt other Hollows rather than humans, mostly because they're now too powerful to be sustained by human spiritual power. Soul Reapers and Quincies have warred for a thousand years over what to do about Hollows, with Soul Reapers purifying them back into the cycle of reincarnation and Quincies permanently destroying them.
Child of Kamiari Month: Kanna and her friends are followed by a malevolent spirit manifested from the negative emotions engendered by the modern age. Feeding on Kanna's grief over her mother's passing, the spirit tries to trick her into giving it the food offerings so it can become an evil god.
Shikabane in Corpse Princess are formed when someone dies with regrets or an attachment to this world, which turns them into a monster.
Akuma in D.Gray-Man are souls of the dead who have been bent to the will of the Millennium Earl. Often grieving for a lost loved one the bereaved person calls their soul down into an Akuma at which point the soul of the lost loved one is imprisoned and has no will of its own. The Millennium Earl orders the newly made Akuma to kill the person that made them an Akuma and wear their body. So they're sad and in pain and become increasingly tortured and tormented as the Akuma develops its own personality around them. The main character, Allen Walker, has a special eye that allows him to see these trapped souls, and aims to release them from their pain... which means killing them. The rest of the Exorcists kill them just because they're monsters, and most of them wouldn't understand or take kindly to Allen's sympathy for them. It's not that the Exorcists don't know how the Akuma are made, but rather that they tend to forget, because they're not constantly seeing it.
One of Noah claims that if an Akuma self-destructs, rather than freeing the soul, the human soul is destroyed. She then demonstrates this to Allen, who watches in horror as the soul is torn into screaming pieces.
More generally, it's stated that the human soul will be released only if the Akuma are killed by an Innocence weapon. Any other method will destroy the soul. It's just that since normal humans don't have a chance of killing an Akuma in the first place, the question never comes up.
The daemonia from Day Break Illusion are a deconstruction of how this trope is usually handled in Magical Girl anime... killing them kills the person they're born from as well.
Miss Michiko from Den-noh Coil, though not technically a monster, is born from Isako's rage and hatred.
In Digimon Adventure 02, Dagomon's realm, the Dark Ocean, is formed by people's dark desires.
Elfen Lied. The Diclonius's DNA Voice could be the result of their constant abuse at the hands of humans.
At a metaphorical level, the homunculi from Fullmetal Alchemist (2003) may be seen as embodying the 'darkness' or despair in the heart of the alchemists who created them and whose memories of a lost loved one they often carry. Or even of the original person or humankind itself. Their Theme Naming following the Seven Deadly Sins helps this interpretation.
In the manga, they are manifestations of Father, the original Homunculus's cruelty and sins - what he is and whether he could be The Heartless himself is up for debate, though.
The Zonder, in the Humongous Mecha series GaoGaiGar are a variation on this; they don't feed on or arise from negative emotions in general so much as they feed on stress specifically. The forms they take on when they transform into Robeasts typically have something to do with the source of their hosts' stress, and destroying them leaves the victim feeling quite mellow.
Magatsuhi from Inuyasha is a spirit born from the wicked and corrupted feelings of the Shikon Jewel.
In King of Thorn, most of the grotesque monsters came to existence as embodiments of the deepest, primal fears of scientists infected with the Medusa virus.
Lady Jewelpet has the Beasts, born of the world's negative emotions and residing inside the Door to Chaos.
The monsters and the second season's Big Bad in Magic Knight Rayearth were born out the despair of Cephiro's citizens.
My-HiME. Yatagarasu, Shiho's Child, is described as residing in the darkness of the human heart.
The Zero-Tails from the second Naruto Shippuden movie is a demon made from the hate or other dark thoughts of others. It can also possess people feeling these emotions.
As part of Naruto's test at the Falls of Truth, the hatred that exists within Naruto's heart is given form for Naruto to confront it. He can't beat it in a battle but realizes the key is to accept the emotions he'd been repressing and avoiding.
The Jikochuus from Doki Doki! PreCure are created with the selfish and petty thoughts of a person's heart without the need of possessing anything, making them a more straight example.
The Saiarks from HappinessCharge Pretty Cure! are a rare inversion: they are created with the positive thoughts of a person that will eventually turn terrible if the monster is not defeated.
The Zetsuborgs from Go! Princess Pretty Cure are another inversion: they are created by stealing the dream of the victim to power up the monster. The dream will be gone forever if the monster is not purified.
The witches of Puella Magi Madoka Magica are embodiments of despair. Specifically, the despair of the Magical Girl they used to be and became unwillingly by being consumed by it. So they are only a part of their character, NOT the whole person. In the ending Madoka Ret Goned witches from existence and the despair of mankind instead manifested in different, separate creatures referred to as majuu/wraiths.
QQ Sweeper has bugs and stains in people's minds that are made of negative emotions and energy, and if they linger too long they'll devour it completely.
A repeated, enigmatic symbol — particularly suggestive shadows — in the movie version of Revolutionary Girl Utena hints that Anthy is missing her heart. However, in an inversion, it is because she is the victim/captive of a monster, not the monster itself. This (probably deliberately) echoes the line about "a doll without a heart" in the TV series.
Nephrite eschews using typical Energy Absorption tactics, preferring to concentrate dark power into a single highly motivated (and increasingly obsessive) person to get the best energy. His predecessor Jadeite worked in a similar way by amplifying negative traits in people, except he worked with large groups of people—Education Mamas, obsessive dieters, etc.—instead of just one person at a time. Zoisite and Kunzite just possess people.
There is also Phages in the final season, and the Lemures of the one before it. The former are humans without a 'Star Seed' whereas the latter are appearently people without their dreams (in the anime version).
The Big Bad of the entire series is a God of Evil born from the malice of all living beings called Chaos, and he ends up having his essence scattered into the hearts of everybody across the universe... to defeat him. Chaos also spawned the Big Bads of all the previous four seasons, being lesser Eldritch Abominations compared to Chaos.
In the Shaman King manga, Oni, which are dangerous spirits conjured by a shaman's ridiculously strong negative emotions. Namely loneliness.
The X-charas in Shugo Chara! can be seen as a form of this: Usually, when a child needs help in fulfilling their dreams, these dreams materialize and become a "Guardian-chara". However, if the child has already GIVEN UP all hope, the dreams instead get corrupted with lack of self-esteem, the feeling of being useless and other negative-emotions and become an "X-chara" instead: A little, black creature, determined to destroy everyone and everything around it with the power of the dream, it was originally supposed to embody. The owner of the X-chara usually falls in a comatose-state, with his or her inner voice mourning about how useless he/she is. Amu usually tries to heal such Charas, by using the powers of the humpty-lock, while others, like Ikuto and Rima (at least in the beginning) prefer to simply destroy them — turning the owner into a child without any hopes for his/her life.
The Gaichuu in Tegami Bachi: Letter Bee. They are large armored insects that lost their heart and are drawn to "heart," such as that contained within letters, which is why being a postman is such a dangerous job in Amberground. The only way to kill them is to use a Shindanjuu to shoot Shindan bullets powered by the user's heart, at the gaps in the Gaichuu's armor.
Unicron's portrayal in Transformers: Armada claims that he feeds on hatred, violence, et cetera. He's a Planet Eater, but the energy from hatred and violence is what gives him the strength to metaphorically get out of bed in the morning. The planet eating is mostly because all life offends him and he wants it gone. This is part of his upgrade from Giant Space Flea from Nowhere in G1 (eventually revealed to have been whipped up by some Mad Scientist on a whim) to God of Evil in the modern TF franchises. He'll exist As Long as There Is Evil (well, so long as there's hate), and his goal is the complete eradication of all universes in The Multiverse, resulting in a Void so empty that even space itself as we think of it no longer exists. He's done this to entire universes before.
At a metaphorical level, Knives in the Trigun manga fulfills the definition too, as he might be viewed as an embodiment of the worst 'sins' of humankind. It is significant that in Trigun Maximum, he starts of as a loving and philanthropic kid and grows extremely fast into a crazed sociopath as a result of trauma or, more symbolically, of absorbing humans' violence and hatred. As such, he fits the Shadow Archetype not only for Vash but also for humans.
In Umi Monogatari, Sedna is revealed to be the combined form of the islanders' sorrow.
Runaway Spirits from The World God Only Knows are a variation of this. They do not originate as The Heartless, but become them after restoring spiritual power by hiding in their victim's bodies.
In the original Yu-Gi-Oh! Duelist Kingdom arc, Ghost Kaiba was the embodiment of Kaiba's negative emotions, given life from Yami's Penalty Game. (Only in the dub; in the original, he was an Eliminator who was either a shapeshifter or a very convincing illusionist.)
