Ecchi (エッチ etchi , pronounced [et.tɕi]) is an often used slang term in the Japanese language for erotic fantasy and sexual innuendoes. As an adjective it is used with the meaning of "dirty", "naughty", "frivolous"; as a verb (ecchi suru), with the meaning to do something dirty, naughty, frivolous or to sleep together; or as a noun, to describe someone that is seen as ecchi. It is a synonym for ero (from Eros) and does not have such a harsh meaning as hentai.
The word is not only common in Japan, it is also used worldwide inside the fandom of Japanese media to describe sexual themes or undertones. While the word ecchi could mean anything from mild to insulting in Japanese language, it is used in Western culture to divide between pornography (hentai) and playful usage of sexualized imagery (ecchi). Works considered as ecchi do not show any sexual intercourse or primary sexual characteristics. Instead, it is up to the imagination of the viewer. Inside such media, it often goes along with fan service in a humorous way. These kinds of sexual themes or undertones can usually be found in comedic Shōnen/Seinen manga and harem anime.
Etymology and use in Japan 
“Hentai” itself was introduced in the Meiji period as a term for change of form or transformation in science and psychology. In context, it was used to refer to disorders such as hysteria or to describe paranormal phenomena like hypnosis and telepathy. Further spreading the word led to the connotation of non standard. In the 1910s, it was used in sexology as the compound expression “hentai seiyoku” (変態性欲, abnormal sexual desire) and became popular within the theory of sexual deviance (Hentai seiyoku ron), published by Eiji Habuto and Jun′ichirō Sawada in 1915. In the 1920s, many publications targeted a broad audience, dealing with deviant sexual appearances, including works related to the Ero Guro Nansensu movement. Matsuzawa calls it a period characterized by a “hetai boom”. In the 1930s began a new western influenced period of censorship which resulted in progressive stop of publication.
After the war, in the 1950s, new journals showed an interest in hentai. With this renewed interest, the word hentai is sometimes written in romaji and it was then that H (pronounced as エッチ, as the pronunciation of the English letter H, //) began to be used as an alternative to “hentai”. In 1952, the magazine Shukan Asahi reported that a woman who was groped by a stranger in a movie theater reacted with "ara etchi yo" ("hey, it's a pervert"). In this context, “etchi” must be understood as sexually inappropriate and is synonymous to iyarashii (嫌らしい, unpleasant, dirty or disgusting) or sukebe (すけべ, a pervert). From that moment, the meaning of “hentai” and “etchi” evolved independently. In the 1960s, etchi started to be used by the youth to refer to sex in general. In 1965, a newspaper reported that primary school children using etchi kotoba (the word sexy). In the 1980s, it was used to mean sex as in the phrase etchi suru (to [make] love). The most common theory states that it derives from the first character of the word hentai (変態),
The word sekkusu is also used in Japan for sex, and Japanese native words for sex (such as 性交 seikō) are often replaced by words of foreign origin such as sekkusu or neologisms such as ecchi. Therefore, ecchi is used as a qualifier for anything that is related to erotic or pornographic content. The nuance of ecchi varies with context, but in general, the word itself is comparable to the English words "naughty" or "dirty" (when used as an adjective). In pornographic context, the word ero and other wordings are preferred over etchi by the media. For example ero-manga (エロ), adult anime (アダルト), or anime / manga for persons over 18 years (18禁アニメ, 18禁), and so on. The prefix "H-" is also sometimes used to refer to pornographic genres: H-anime, H-manga, etc.
Western usage 
In western nations, the spelling as ecchi is preferred, although it does not follow the Hepburn method. This has its origin in the foreign fandom of manga and anime, which used a different method (or no method at all) to transcribe the word. In comparison to hentai, which "is anime erotica", it was adapted "among coy fans and distributors who preferred to use a foreign term for their pornography" in the west, the abbreviation ecchi is seen as softer in meaning than the full term. Calling a Japanese boy e(t/c)chi might be flirtatious, as opposed to the more insulting hentai.
[...] Bezeichnet erotische Darstellungen. Im Vergleich zu Hentai weniger explizit.
[...] [Ecchi] refers to erotic depictions. In comparison to hentai, it is less explicit.—Sebastian Keller, Der Manga und seine Szene in Deutschland von den Anfängen in den 1980er Jahren bis zur Gegenwart: Manga- mehr als nur große Augen
The term ecchi is used to describe a category of manga and anime with sexually oriented content, that is common in works aimed at a predominantly male audience (shōnen or seinen). But also works aimed at a female audience can contain scenes which are seen as ecchi. Examples are R-18 Love Report! from Emiko Sugi and Oruchuban Ebichu from Risa Itō, which are aimed at the shōjo and josei audience, but contain rather explicit content.
This can be conversations with sexual references or misunderstandings about sexuality in dialogs (double meaning, words taken out of context), misunderstandings in visual depictions (the position or pose of a character is suggestive), clothing (underwear, cosplay, fetish clothing, etc.), nudity (ripped apart clothing, wet clothing, clothing malfuncations, etc.) and the portrayal of certain actions (touch or look at parts of the body). This kind of sexuality is commonly used for comical effect. A typical example scene would contain a male protagonist that accidentally enters a women-only bath or trips over a female character, leaving the impression of sexual harassment.
The concept of ecchi is very close related to fan service. While fan service describes every aspect to please the fans, ecchi relates to sexual themes. A special kind of fan service, that is usually bound or justified by the narrative.
Typical examples 
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There are many possibilities to classify a work itself as ecchi, but this elements have to occur quite often (for example in all episodes of an anime). Graphically speaking, different techniques are used to show sexy pictures, usually by revealing parts of the female body. Some of these patterns are recurrent, such as scenes in a shower, onsen, or fighting scenes in which clothes are torn apart by weapons or magic. This involves the back, buttocks or even breasts and panchira. The imagination of characters is also a common excuse to show its sexual fantasies, as well as transformation scenes of magical girls. In the end, any excuse is valid to show a character partially or completely nude.
The level of nudity varies strongly between works, because of the intended audience and the preferences of the authors. In some cases, though the breasts are shown on the screen, nipples and genitals are obscured by smoke, moss, hair, clothing, a decorative element, a light effect, etc. This kind of censorship was typical for Lala in To Love-Ru, Blair in Soul Eater or even Asuka Langley Soryu from Neon Genesis Evangelion. In Ladies versus Butlers! and other anime, the nipples are clearly visible through clothing, no matter how thick it is.
A typical reaction to nudity is nosebleeding, which represents sexual arousal. Rather extreme examples are Baka to Test to Shōkanjū and Maria†Holic. In both cases, the characters “nearly die” because of constant blood loss. In Baka to Test to Shōkanjū, the male characters are confronted with nice girls (including the trap Hideyoshi Kinoshita). In Maria†Holic, the main protagonist is the lesbian Kanako Miyamae. Despite her forbidden love, she joins an all-girls school, which leads often to excessive nosebleed, unable to stand up to her adversary, Maria. Despite the fact she knows that Maria is a man (also a trap), she still falls for his feminine appearance.
The visibility of the underwear (panties) is one common motif. It often leads to strange reactions between a female and the male protagonist, who would accidentally (or not) look at the underwear. The reaction can be quite varied, depending on the color and style of pantsu, but usually the male is punished for looking, regardless of the reason. The color and style of the pantsu is not chosen at random. Both are seen as an indication for the female's character. Innocent females wear simple white or kawaii themed underwear (with hearts or similar motifs), shy girls prefer the shimapan (striped panties); in some cultures red is seen as 'of the devil' or "naughty," etc.
The pantsu theme itself is so popular, that it is an important object in anime like Chobits or Sora no Otoshimono. Coincidently, both anime's fourth episodes are based on the pantsu theme as a narrative element alone. The anime Panty & Stocking with Garterbelt goes another step further, in which pantsu is used as a weapon. But even if the pantsu is not the main topic itself, it is often shown due to a "careful choice" of camera angles. In this case, it can be rightfully called fan service, since it is not needed for the story itself.
Sexual intercourse 
Normally, there is no sex in manga or anime which are considered ecchi. Such works are known as hentai, a form of animated pornography. But it is still possible to make a pun on sexual intercourse through misunderstandings. One simple example would be two characters searching for some kind of item, which appears from the outside, only showing the silhouette, as if both would have an actual intercourse.
- Sebastian Keller: Der Manga und seine Szene in Deutschland von den Anfängen in den 1980er Jahren bis zur Gegenwart: Manga- mehr als nur große Augen, GRIN Verlag, 2008, ISBN 978-3-638-94029-0, p. 127
- Robin E. Brenner: Understanding manga and anime. Libraries Unlimited, 2007, ISBN 978-1-59158-332-5, p. 89.
- Ask John: Why Do Americans Hate Harem Anime?. animenation.net. May 20. 2005. Note: fan service and ecchi are often considered the same in wording
- After the sources of the article Hepburn romanization. In Hepburn, the sokuon (っ, small tsu) is romanized t before ch.
- Hikaru, Saitō (2004). Hentai—H. Sei no yōgoshū (Kansai seiyoku kenkyūkai ed.). Kōdansha gendaishinsho. pp. 45–58.
- Robertson, Jennifer (1991). Gender and the State in Japan. Theatrical Resistance, Theatres of Restraint: The Takarazuka Revue and the "State Theatre" Movement in Japan. Vol. 64. The George Washington University Institute for Ethnographic Research. pp. 165–177.
- Robertson, Jennifer (1999). Dying to Tell: Sexuality and Suicide in Imperial Japan. Vol.25. The University of Chicago Press. p. 21.
- Reichert, Jim. Deviance and Social Darwinism in Edogawa Ranpo's Erotic-Grotesque Thriller "Kotō no oni". Journal of Japanese Studies. Vol. 27. The Society for Japanese Studies. p. 128.
- Goichi Matsuzawa (1997). Meiji, Taishō, Shōwa, kindai fūzoku shuppan no rekishi, Ero no hon. Tokyo. Wani no ana. p. 55
- Sabine Frühstück (2003). Colonizing Sex: Sexology and Social Control in Modern Japan. University of California Press. ISBN 0-520-23548-7. p. 15
- Mark McLelland (2006). A Short History of 'Hentai'. In: Intersections: Gender, History and Culture in the Asian Context. Vol. 12.
- Cunningham, Phillip J. (1995). Zakennayo!. Penguin Group. p. 30.
- "エッチ" (in Japanese). 語源由来辞典.
- Jonathan Clements, Helen McCarthy: The anime encyclopedia: a guide to Japanese animation since 1917, Edition 2, Stone Bridge Press, 2006, University of California, ISBN 1-933330-10-4, p. 30
- Robin E. Brenner: Understanding Manga and Anime. Libraries Unlimited, 2007, ISBN 1-59158-332-2, p. 295
- Steiff, Josef; Tamplin, Tristan D. (2010). Anime and Philosophy. Popular Culture and Philosophy. Vol. 47. Open Court Puplishing. ISBN 978-0-8126-9670-7.