This school swimsuit
But it is more of a fetish, really.

Having lived in Japan for a number of years and having traveled all over Asia, I would say that staying on the modest side will ensure that you do not offend or find yourself feeling uncomfortable.

Lived there for six years and I can guarantee that a teeny weeny bikini at the beach won’t raise eyebrows. A thong might be a step too far, so maybe don’t go the whole Miami route.

Just my humble opinion after years of being a beach bum in Japan (in Kyushu – near Miyazaki where surfing and hanging out at the beach are a common all weekend activity) but.. Japanese swim suits tend to be more about being able to be active & athletic (for example, men wear Speedos very often because that’s what they’re used to from their days of swimming during physical education at school) than to make a fashion statement.
Bikinis are common at the beach for girls – but at @Rheto_Ric suggests—not thongs.