The origin of canpaign girl is a bit obscure and no one is sure but they say it was a girl handing out free cigarette on the street for promotion. They wore swim wear (or something very similar to swim wear such as tunk top and mini skirt). These campaign girls influenced and inspired some people to create Race Queen, Trade Show Campain Girls, and Swim Wear Campaign Girls. Among them, the most pecurier and interesting campaign girls should be swim wear campaign girls because they are very difficult to become and also it is a means to promote products and company reputation but also promote campaign girls themselves.
The official start of swim wear campaign girl was back in 1966, A cosmetics maker, Shiseido used a popular western look actress called Maeda Bibari for their Summer campaign. At that time, campaign girls were selected from popular actresses or models and they had been already stars.

Maeda Bibari, official page at http://www.creemintl.co.jp/indivisual_bibari.htm
However, in 1970, fabric/clothes maker Teijin used relatively unknown model called Akikawa Risa. She showed up regularly in mid-night TV programs such as 11PM, but was not many people expected her to be in a major campaign with a fairly large company like Teijin. Akikawa Risa got popularity because of Teijin campaign and became a main strem model afterwards. There are about 10 major companies employee yourg girls for their regular Summer campaign right now but each company hire only one each, and to become a swim wear campaign girl is very hard.
Since then, swim wear campaign girls were somewhat of highly regarded status for start-up models/actresses to step up their carreer drastically. There are plenty of popular models/actresses to name; Maryanne (Shiseido, 1981), Saito Keiko (JAL, 1982), Washio Isako (ANA, 1985), Iijima Naoko (Kanebo, Kirin Beer, 1990), Manabe Kaori (Toyobo, 2000). Some of them were even university students or semi-pro models at the time they were hired for campaign.
Manabe Kaori, was a university student and scouted on the street. Her blog page is at http://manabekawori.cocolog-nifty.com/blog/
Now, it seems swim wear campaign girls does not have the magic they used to have, but still it is a dream to many young girls and models.