Extended shinjitai (拡張新字体 kakuchō shinjitai , lit. extended new character form) is the extension of the shinjitai simplification method to hyōgaiji (表外字): kanji not included in the jōyō kanji list. They are unofficial characters: the official forms of hyōgaiji are kyūjitai (traditional characters).
Simplified forms 
When the 1850 character-long tōyō kanji list was produced in 1949, many characters were simplified from their original forms, and the new simpler forms became the standard kanji used in Japanese writing. For instance, the characters 學, 國, and 體, became 学, 国, and 体, respectively. The jōyō kanji list, issued in 1981, contained additional simplifications such as 罐, 螢, and 龍, becoming 缶, 蛍, and 竜. In addition, the character 燈, which had already been reformed once during the formation of the tōyō kanji list, became 灯. A total of 357 characters were reformed from kyūjitai (old character form) to become shinjitai (new character form) when the jōyō kanji list was created (辨, 瓣, and 辯, were merged into a single character: 弁, bringing the total number of new shinjitai down to 355).
However, as a result of adopting simplified characters, kanji that shared the same structural elements (radicals) were not all simplified in the same way. For instance, 賣, 續, and 讀, which were included in the list, were simplified as 売, 続, and 読, but the hyōgaiji 贖, 犢, and 牘, which contain the same element (賣) as the three previous kanji, were not given simplified forms. This problem arose from reforming characters on an individual basis rather than decomposing all characters into radicals and other constructs as was done for simplified Chinese characters.
Creation of extended shinjitai 
The Asahi Shimbun newspaper developed its own script known as Asahi characters, which applied the rationale of simplification to characters other than jōyō kanji. In this script, the right element of the three previously mentioned unsimplified characters (贖, 犢, and 牘) were all simplified as 売. Characters that were simplified in this way are called extended shinjitai, as simplification was extended to characters outside of the jōyō kanji list.
JIS X 0208, created in 1983, was the first JIS character set to extensively use extended shinjitai, adopting simplifications for a large number of previously unsimplified characters. In total, 299 characters such as 鷗, 瀆, 潑, 逢, 飴 (301, including 曾 and 訛) were simplified from their original forms. Simplified forms had never been used in printing these characters prior to this reform. However, the character set became subject to criticism when it was revealed that the character 鷗 in the name "森鷗外" (Mori Ōgai; a famous Japanese poet and novelist) could only be represented in word processors in its simplified form (鴎).
Reduction of extended shinjitai 
Established in 1990, the JIS X 0212 set of auxiliary characters supplemented the previous character set by including both the traditional and simplified forms of certain characters. For instance, the traditional 鷗, 瀆, and 潑 characters were included in addition to the simplified 鴎, 涜, and 溌 characters. However, usage of these auxiliary characters in the Shift JIS computer encoding was not take into consideration, and most word processors remained unable to display these traditional characters. The Japanese Language Council meeting of 1992 confirmed the need for a unified character set that could be used in all computers and word processors.
Released in February, 2000, the JIS X 0213-2000 character set was presented as a solution to the problems of the previous character set, as the Shift JIS encoding was expanded to re-include traditional characters such as 鷗, 瀆, and 潑. In December of the same year, the Japanese Language Council compiled a list of kanji not included on the jōyō kanji list, and announced certain standards that would be used for all printed script. The creation of this list made it clear that extended shinjitai would not be used for kanji other than jōyō kanji, leading to an increased move towards reducing the use of extended shinjitai.
JIS X 0213-2004 (released in 2004) made minor modifications to the script, changing character shapes and strokes. For characters that are not in the jōyō kanji list, the single-dot shinnyō radical was changed into a double-dot radical. The Windows Vista operating system, released in January, 2007, conformed to these modifications, but confusion resulted in cases where the single-dot radical was automatically changed to the double-dot radical in surnames written using the character 辻.
The Asahi Shimbun newspaper also modified its characters to conform to the new standards, and altered their Asahi characters in January, 2007.
- This article incorporates information from