Japanese Preppy is, as the name implies, a Japanese take on classic American Preppy style. Although the look seeks to emulate the American look, it did not take off as a style until after Japanese specific preppy brands began to market to Japan.
Japanese Preppy is part of the larger, Ametora umbrella.
Japanese Preppy has a self-explanatory name, taking its name from the American Preppy style. There is also a female-focused variant of the name, called joshi daisei (女子大生) meaning female college student. 
The Japanese Preppy style is greatly influenced, and almost a mimicry of, the American Preppy style. However, the Japanese version did not gain prominence with the rising of the trend overseas, but rather was basically created by Kensuke Ishizu. Ishizu attempted to build the style in the 1960s and 1970s, but was unsuccessful in helping the style catch on until the 1980s, when he launched his brand VANS. As such, he is created as the father of Japanese Preppy fashion. 
Although the style has existed in small communities since the creation of the style in America, it is not considered an active style until 1981 when it became a larger trend. The style is still active to this day in Japan, and although it is no longer a mass trend as it was in the 1980s, it still has a significant following and is a permanent part in the fashion scene, much as it is in America. 
Style Basics Edit
The Japanese Preppy style borrows heavily from American preppy fashion, pulling extensively from American sources such as "Take Ivy,” “Ivy Illustrated,” and “The Official Preppy Handbook," which are all considered guides for the style in Japan and abroad. 
Popular looks in the style as it exists in Japan are cardigans and sweaters, lettermen jackets, leather shoes, tailored clothing, suit pants and jackets, dress pants, turtlenecks, button-up shirts, preppy dresses for women, and bomber jackets.
Newer Preppy styles may take inspiration from modern Japanese trends, but most tend to stick closely to the traditional, idealized style, as opposed to updating and changing it.
Brands & Shops Edit
Japanese Preppy has had a large influence on fashion in Japan. For instance, the fashion magazine Cancam, founded in 1982 comes from this movement. The magazine is still active, although now it focuses on broader fashion themes, instead of only Preppy style. 
International Preppy brands, especially big names, have also long been popular, such as Ralph Lauren.
Of course, VAN is a major leader in the style, having been created by Kensuke Ishizu, the first to bring the style to Japan.