Written Japanese has three different scripts — hiragana, katakana and kanji — so you wouldn’t think there’d be room for any more. But you’d be wrong.
ローマ字 (rōmaji, the Roman alphabet) is often considered the fourth Japanese script, and has carved out a space for itself in everyday life. For example, recently it popped up in the name for the Tokyu Oimachi Line’s new seat reservation program, Qシート (kyū shiito, Q seat). The letter “Q” is meant to stand for the English words “quick” and “quality,” and also provides an alliterative link with the 東急 (Tōkyū, Tokyu) Corporation that operates the line.
Other common made-in-Japan acronyms composed of English words include OL (ōeru, office lady), which is a female office clerk or secretary; and LDK (erudiikē), a combined living-dining-kitchen area in a house or apartment. More colloquially, NG (enujii, no good) can be used as an expression of disapproval, to indicate that something is not allowed. Although made up of English words, some Japanese are still surprised to learn these terms aren’t that familiar to English speakers outside of Japan.
Rōmaji can also be used to create acronyms from Japanese words, such as JK (jēkē) for 女子高生 (jyoshi kōsei, female high school student), and sometimes even JC (jēshī) for their junior high school counterparts. Another term once popular with this demographic was the acronym KY (kēwai) representing the phrase 空気が読めない (kūki ga yomenai, unable to read the air), which is used to refer to someone who’s unable to read the room. That acronym is feeling its age now, and you might be accused of being a bit KY yourself if you try to drop it into a conversation these days.
Another letter that has taken on new meaning in Japan is the letter “H” (エッチ, ecchi). The first letter in the word “hentai” (変態, perversion), it has come to be associated with sex in terms such as Hな話 (ecchina hanashi, erotic story). However, today’s youth are more likely to use a different loan word, エロい (eroi, erotic) instead of Hな.
Rōmaji is also used in more generic terms such as Yシャツ(wai shatsu), which might cause people who are not familiar with the term to puzzle over what the “Y” could possibly stand for. In this case, however, the letter represents the first sound in “white (business) shirt.” The word “wai shatsu” is an interesting departure from the usual katakana-ization of the color ホワイト(howaito, white), suggesting that wai shatsu as entered the language by being heard, rather than being seen in written language. After all, ワイシャツ sounds slightly closer to the English term than ホワイトシャツ when spoken quickly.
Another example that’s a bit less obvious is the use of the letter “W” to represent the word “double,” in terms such as Wカツ弁当 (daburu katsu bentō, double breaded pork cutlet bento box), or ハッピーWポイント開催 (happii daburu pointo kaisai, happy double-points opening offer). Like the “Y” in Yシャツ, the “W” is being used for (the first half of) its sound, rather than as a word in an acronym. Since rōmaji letters sometimes represent whole words and sometimes just sounds, parallels can be seen with how kanji are used in Japanese: sometimes for an integral meaning, and sometimes just for a particular sound or reading of the character. It is perhaps from this basis that the use of rōmaji letters has fit so neatly into the Japanese writing system.
With your new knowledge of how rōmaji can be used in Japanese, a sentence like OLによれば、近所のクリーニング屋では、YシャツのWポイントキャンペーンを実施中だそうです (Ōeru ni yoreba, kinjo no kuriiningu-ya dewa, waishatsu no dabburu pointo kyanpēn o jisshichū da sō desu, According to the secretary, the cleaners next door are having a double-savings campaign on business shirts) or JKがHな雑誌に登場することはNGだね (Jēkē ga ecchina zasshi ni tōjō suru koto wa enujii da ne, It’s not OK for female high school students to appear in risque magazines) will look more and more Japanese despite the Roman letters.