Illusion is the condition of being deceived by a false perception or belief, something that deceives by producing a false or misleading impression of reality.
Illusions are not every single misguidance, for example, if a character is something called ambigous gender (like Haku from Naruto), even though his appearance is misleading impression of reality, it still isn't an illusion.
In anime/manga world where almost everything can be interpretated as a misleading impression of reality, still exists illusions as a concept in which a certain character is manipulating other people senses in orther to achieve his goals.
I tried to find some pictures of those illusions, but it's kinda hard to track them all down, and especially illusions of those characters that I haven't actually watched yet.
1. Ai Enma - (Ai can create large, intricate illusions, which she often does to frighten her victims before taking them to Hell. She also creates illusions at other times, like when trying to convince Tsugumi Shibata to send her father to hell.)
2. Asura – (He presides over the attributes that drives men towards madness, which in his particular case is the possession of "Terror".The Madness he employs awakens the insanity within others. His Madness can also even cause illusions and hallucinations.)
3. Ban Mido – (he can utilize the Evil Eye (Jagan), a power which allows him to make anyone he makes eye contact with to watch a one minute long illusion, however, it should only be used three times per day. Furthermore, while the illusion only lasts for one minute, should Ban will it, the one affected by the Jagan can be placed inside a time-warp zone via the illusion created by the technique, meaning that to them, one minute in real life could last up to several hours in the Jagan's influence.)
4. Carmilla – (She can use illusions to break her targets mind.)
5. Chrome Dokuro – (Chrome is a talented illusionist and fighter, something that Mukuro has pointed out, stating that she has a quality to become independent soldier. Even though at first she's mostly assisted by Mukuro, her own illusions gradually improves to the point only an expert can see through it, as stated by Mammon. This further proven when she's able to create illusionary organs with her own power and supported Mukuro's illusions that even Mukuro commented to be stronger from Fran.)
6. Cross Marian – (Cross is able to use magic to control Maria's corpse and Maria uses her song to create illusions that can conceal the presence of others.)
7. Daemon Spade – (The power of the illusion is comparable in both appearance and power to the actual object. It is also shown that he can disable the illusions of other people)
8. Danzo Shimura – (Danzo is able to use his jutsu, Izanagi, to resurrect himself again. It's explained that Izanagi blurs reality and illusion, and that for 60 seconds, Danzo is invincible because any injury or death caused will be changed into an illusion)
9. Demon Eyes Kyo – (His sword style is The Sword of a Devilish Wind which was taught to him by Muramasa. It teaches standard fencing skills and defense, but they are far more powerful than any of the skills of other sword styles. It is the most powerful sword school in the Mibu Clan. It utilizes attacks that can cut air and create illusions)
10. Enjin Hiizumi – (Enjin can manipulate the thoughts of people on a massive scale. He was able to make the entire population of Sakurashin Town not think about a house or even see it. He also made the residents of Sakurashin Town unable to leave via telepathic control. In addition he's capable of casting illusions to change his appearance or to simply confuse people. Once he disguised himself as a human in a different town without anyone noticing it.)
11. Fran – (He can use Reality illusion gloves - Gloves that allow Flan to make illusions into real, solid objects)
12. Fukasaku and Shima – (Shima and Fukasaku are capable of using a very powerful genjutsu called Demonic Illusion: Toad Confrontation Chant. This ability cancelled out Jiraiya's lack of aptitude for genjutsu, making their combination much stronger. However, this genjutsu takes time. Also, in order to use this technique, both Shima and Fukasaku must adjust their voices and harmonise with each other (something neither of them seems happy about doing). When finally applied, it attacks the opponent's sense of hearing, and will completely paralyse the target(s) body.)
13. Genkishi – (He can use a large number of slugs that create Illusions altering the landscape around opponents. They can move independently or as a group towards a target and explode on impact while remaining hidden. He also have the illusion sword that can create multiple copies of itself as well as mist flames, to be used as countless projectiles)
14. Hisahide Matsunaga – (By releasing some kind of shiny butterflies she can make her target think that everything is a dream, thus making them more vulnerable to physical attacks.)
15. Itachi Uchiha – (Itachi was especially known for his skills with Sharingan-based genjutsu, and was considered one of the Uchiha's most powerful users. His skill was such that he could cast one by merely pointing atsomeone or turning opponents' genjutsu against them.)
16. Kaguya Hime – (In addition to the Mirror Illusions Kaguya is capable of conjuring, she is also capable of masking her own appearance behind a fair-seeming visage, cloaking her true demon form. When Kaguya first awakens after Naraku's "death," she raises the Dream Castle of the Pentacle Mirror from the bottom of Lake Motosu. However, this castle is only an illusion. The real castle lies within another dimension inside the "Realm of the Night.")
17. Kirito – (In ALO he has the ablility to wrap himself in an illusion and make himself look like any monster he has seen before. The first time he did this, he morphed into a high lvl boss demon. the illusions are real since he was able to pick up other players and bite their heads off.)
18. Kouga Kuchiki – (Muramasa can control other Zanpakuto, but its ability is just apart of Kouga's own special ability. He can send his Reiatsu into his enemies and throw off all of their senses. He then has complete control over what they perceive. Thus making it so his opponent cannot even see him clearly though he is right in front of him. Kouga states it is so much more than simple illusions. This power can be negated by one closing their "hearts" off before challenging him.)
19. Kurenai Yuuhi – (The full extent of Kurenai's abilities are predominantly unknown. But, her skill with genjutsu is so vast that it is said to rival even those of Itachi Uchiha. Most of her techniques focus around flora; primarily using large trees to bind opponents as well as flower petals for various reasons. She is also able to simultaneously affect multiple opponents with her techniques)
20. Mukuro Rokudo – (Being a skillful user of illusions, he is not easily deceived by illusions that are cast by others, possessing a highly perceptive mind and also able to dispel other illusions cast by illusionists. Mukuro uses the glove invented by Verde that able to turn illusions into reality to create man-eating crows that eat the opponent.)
21. Mystogan – (Mystogan first plants his five staves into the ground, creating the illusion that the enemy is propelled several hundred meters into the air. The enemy is then tied up with four belts and a demon breaks through the sky, reaching to attack the enemy. )
22. Nami – ( The Clima-Tact has been used to create mirages of herself making a fata morgana.)
23. Obito Uchiha – (Obito can keep his targets under genjutsu while they are confined inside this pocket dimension and thus, keep them incapacitated for extended durations. He also intends to create ultimate illusion for every person on the planet using the Moon as a illusion caster.)
24. Orochimaru – (His "Killer Intent," is an illusion technique that makes his opponent experience their own death.)
25. Ririn – (Ririn was designed with the unique ability to make illusions. She can change the appearance of an environment, which she uses to confuse opponents)
26. Road Kamelot – (Road becomes enraged and decides to punish Lavi for Allen's deed. She forces Allen and the others to stand idly by as she attempts to break Lavi's mind, threatening death if they make even the smallest movement. Redoubling her efforts in the dreamworld, Lavi is forced to fight illusions of his friends while his other self insists he is not suitable to be a bookman. His mind is finally shattered as Lavi is run through by illusions of his closest friends.)
27. Saizo Kirigakure – He is able to create afterimage-like illusions of himself (presumably by bending light).
27a. Saizou Kirigakure - Joujuu Senjin!! Mushibugyo - He's a leader of the Ten Crucifix Insects. As a former ninja of Iga, he was a master of illusion. As a cricket, he beats his wings, and the sound from his wing beats messes with his opponent's five senses. As a result, it can hypnotize his opponents and believe the illusions are real.
28. Sasuke Uchiha – (At first he was not so good with using genjutsu, but after he got new pair of eyes from his brother Itachi, he was able to make some illusions. Still not as good as Itachi was, but he was able to win against Danzo because he made an illusion of his arm, making him think he still have his izanagi.)
29. Shinji Hirako – (Shinji describes the release technique as something like a trump card. Up and down, left and right as well as forward and backward are reversed. However, it is not just the sense of direction that is changed; the opponent's eyesight, direction of incoming attacks, and injury locations are also inverted. Shinji claims that countering the damage from the inverted directions simply by processing it all within the mind is not possible.)
30. Shippo – (The toy snake he possesses is transformed into a large snake, usually attacking the opponent. It is only an illusion, and is discovered quickly. Fox Magic: The skill to create illusions and make someone feel pain and/or weight as if it were real. This technique is highly effective in stopping enemies in their tracks. He can also create illusory duplicates of himself)
31. Shukuro Tsukishima – (Book of the End has the ability to split the past of whomever it cuts. This ability works not by manipulating time and memories, but by literally inserting Tsukishima's presence into the victim’s history. Victims of this power recognize Tsukishima as someone closely connected to their personal lives, whether it is as family, friend, or lover. He can even usurp the roles of other individuals in the victims’ pasts.)
32. Sousuke Aizen – (Though it can be said that the majority of his tactics rely heavily on his Zanpakutō's special ability, there are few tactics better than manipulating all the senses of your opponents, making it easier for one to attack.)
33. Tayuya – (Another one of her abilities was performing sound-based genjutsu, such as Demonic Flute: Phantom Sound Chains. Since it was transmitted through the sound of her flute, it had an extremely long range and power, and could affect the opponent even if she didn't know their exact location.)
34. Thanatos – (Appearently Thanatos is an omnipotent being capable of manipulation people senses to make an ultimate utopia illusion.)
35. Torikabuto – (Torikabuto was a very powerful Illusionist, capable of combining them with Box Weapons and even fooling the Vongola Hyper Intuition.)
36. Viper – (His most commonly seen used Illusions are Illusions of clones of himself and the Illusion of tentacles. One of Viper's illusions that sets a rule on the target of which the illusion is cast on. If the rule is broken by the target, the target is instantly damaged with a multitude of deep cuts.)
37. Yuu Kanda – (First Illusion: Netherworld Insects: Kanda swings his sword and releases a small swarm of supernatural creatures that devour his opponents. Double Illusion Sword: Kanda covers his sword and scabbard in a coat of energy and generates an energy blade, creating two impossibly sharp weapons. The second blade that he creates over his scabbard can also be just a pure energy blade if the scabbard is not used.)
38. Zorin Blitz – (Her signature power is her ability to create illusions, seemingly facilitated by the third eye on her right palm. These illusions include creating an enormous copy of herself (taller than Hellsing Manor) and showing her victim a painful or distracting memory. While a victim is trapped in an illusion, Zorin appears to be capable of reading their minds/souls to tailor her illusions for maximum damage.)
39. Zoroark – (The characters are able to transform into different Pokémon at will using their "Illusion" abilities. It has the power to delude many people at one time. It protects its den by displaying an illusory landscape.)
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