Sayaka Ando — gravure idol, commonly referred to as a bikini model/idol.
But what exactly is a gravure idol?
“…is a Japanese female model who primarily models on magazines, especially those marketed to men, photobooks or DVDs. Gravure idols, in most cases, emphasize their sexual attractiveness and often model in swimsuits or lingerie.” (Wiki)
First three pics above are least revealing; links below show more gravure (bikini/lingerie) idol material:
aparoo says Sayaka is a better idol than Justin Beiber