It depends on situations but if you are obviously braless on a street at daytime, someone kind or meddlesome may reprove you, on a crowded train, you may be aimed at with malicious eyes, in an entertainment district at evening, you may be mistaken for a girl entertainer. As AK pointed out, you might have unplesasant stares. I am planning to go to Japan this summer. I will definitely wear a bra! I agree with the three commenting above. Bras here actually tend to be extra thick in order to avoid the slightest possibility of the shape of the nipples showing through.
Emersyn. Age: 27.
I am planning to go to Japan this summer.
Harper. Age: 25.
Marina Yamasaki - braless & bouncing saggy tit
Just don't let things be just too obvious, you might send out the wrong signals. As AK pointed out, you might have unplesasant stares. Depends on sorry to put it blunt how much things may be seen through. Generally, as along as a person is wearing clothing, just being braless doesn't constitute a crime in Japan.