Tentacle Monster

The Tentacle Monster is a specified type of creature that is defined by their sexual appetite and their possession of tentacle appendages. While exceptions do exists, these creatures are largely depicted as sexually predatory and completely alien in comparison to the human form.

Genre History
The tentacle monster's prominence in Japanese erotic literature largely arose due to influence from the aesthetics of censorship in western civilisation.

One of the earliest examples of Tentacle Monster erotica is a shunga illustration (erotic artwork that was commonly accepted as non-taboo in Japanese life) from the 1814 novel Kinoe no komatsu; popularly known as  where a Japanese pearl diver is depicted being captured, enveloped and forced into receiving cunnilingus from one octopi as another gropes and kisses her. While western audiences often interpret Hokusai's illustration as rape, Japanese audiences view it as consensual, particularly as the dialogue in the illustration shows both the diver and the two octopi expressing their enjoyment with the situation; with the large octopus exclaiming its delight in finally ensnaring her, complimenting how "ripe and full" her "bobo" is and expressing his desire to drag her beneath the ocean to the Dragon Palace to envelop her, while the diver herself exclaims how pleasurable being sucked by the octopus is and encourages the octopi to touch her and continue "sucking at the mouth of her womb" as she orgasms. The Dream of the Fisherman's Wife is not the only work of Edo-period art to depict erotic relations between a woman and an octopus. Some early carvings show cephalopods fondling nude women.

In the late 19th century (1882) Joshua Handley, an English artist and photographer for erotic literature in Paris, traveled to Japan to document the less well-known aspects of the Japanese and their culture. This resulted in him viewing the Dream of the Fisherman's Wife and forming an obsession with cephalopod erotica. Handley attempted multiple times to publish illustrations similar to Dream of the Fisherman's Wife in England, even coming up with some of his own involving female pearl divers, shipwrecked gentlewomen or unwary bathers who would fall prey to an octopus and become enmeshed in its tentacles, however, his publisher was appalled by the content. Not by the tentacles and rape (which they believed would appeal to people with "darker sensibilities") but at the notion that the women in the stories actually enjoyed themselves as they succumbed to tentacles and suckers. Handley eventually gave up trying to produce his artworks and, ashamed of his tastes, abandoned all involvement with pornography and turned to illustrating children's books under his mother's maiden name.

As part of the Meiji Restoration (1868-1912), which saw Japan adopt many aspects of western civilisation in order to "become more civilised", Japan adopted new laws influence by Victorian-era Europe to forbid public nudity (where previously Japanese men and women were free to walk around topless or in loin-cloths should they wish) and multi-gender public baths. During this era, creation of traditional Shunga art was also restricted.

Restrictions increased further during the years surrounding World War II, forbidding all erotic art and literature, until post-WWII when the occupying Allied Forces imposed a number of reforms on the Japanese government; which included a lessening on restrictions of erotic expression. Due to this, while “obscenity” (which included depictions of exposed genitalia) was still illegal to portray without censorship (which led to the creation of the "Black Bar" and "Mosaic Blur" to censor the offending material), the diversity of sexual acts that were now permissible to use led to a rise in erotic fiction.

By 1990, in their pursuit to create new material, erotic artists had devoted their efforts in creating new ways to either circumvent the "obscenity law" or to otherwise eroticize otherwise banal subjects, however, it was artist Toshio Maeda who is credited with coming upon the notion that, while the law forbid depicting traditional human genital-to-genital intercourse, it did not forbid depicting pseudo-genital-to-genital intercourse. Following this revelation, Maeda creates a new erotic manga that depicts women in sexual situations with non-human creatures who use tentacle-appendages to penetrate and otherwise assail the female characters. As the monsters did not have a defined gender and did not have/use human genitals (as they are strictly defined by the law), the sexual acts could be shown uncensored. Furthermore, the diverse sexual utility that these fictional creatures brought to the conceptual table meant that numerous fetishes could be believably implemented at the same time.

The earliest animated form of tentacle assault was in the 1985 hentai OVA, though the scene in question was removed when the OVA was re-released in a non-hentai form. The first non-hentai anime production portraying tentacle assault was the 1986 anime OVA, which featured a female Chronos soldier named Valcuria being enveloped by the 2nd biological Guyver suit when the suit produced tentacles to fuse with her, finding and penetrating all of her orifices in the process.

Toshio Maeda produced 1986's, which popularized the trope of tentacle rape and featured a scene where a nurse gets torn apart by the tentacles assailing her which grew to serve as the template for tentacle rape scenes. In 1989, Toshio Maeda's manga Demon Beast Invasion created what might be called the modern Japanese paradigm of tentacle porn, in which the elements of sexual assault are emphasized. Maeda would go on to create 1992's and 1995's, both of which are additionally considered staples in the Tentacle rape genre.

The use of tentacles in live-action films started in American B-movie horror films and has since migrated back to Japan. Producer Roger Corman used the concept of tentacle rape in a brief scene in his 1970 film and he would again use tentacle rape while producing  in 1980. The scene was so graphic that the film's director, B. D. Clark, refused to helm it and the actress whose character would become the victim refused to do the full nudity required, so Corman directed the scene himself and used a body double for some of the more graphic shots.

Trivia

 * The tentacle monster is a source of great amusement for the anime/manga fandom, is often brought up in a joking manner and is subject to much parody from inside and outside the anime community. Unfortunately, it is also used by those outside of the fandom to exemplify anime and manga (and those that enjoy them) as being a perverse and inappropriate medium.