The stereotypical Hairstyle for Japanese girls is front bangs. The majority of girls have the foreheads hidden by a curtain of hair.
(Popular Idols from the group Nogizaka 48)
Oddly, it wasn't always like this. In fact, Before the 60s Japanese women generally showed their foreheads.
(Japanese girls, 1953, wearing old-style sailor school uniforms.)
The trend for bangs started in the 60s as this advertisement shows.
What is behind all of this? It's a combination of culture and social attitudes. Traditionally, only very young boys and girls had bangs. Depending on the period, people of different ages had different haircuts.
(Baby haircut 15th Century)
As one hit puberty, one moved on to an adult haircut that showed the forehead. To have bangs after 16 was inappropriate.
(Scene from a Samurai movie)
In Modern Japan, the focus has been on cute and youthful so that people do not feel that young things are age inappropriate. Adulthood includes s*x appeal which is embarrassing for Japanese girls. Showing the forehead is like showing cleavage or wearing a sexy bikini. Generally speaking, the girls that do show their forehead are less Kawaii types. Another reason bangs are popular in Japan is that it has fashion advantages. For one thing, it makes the person look younger by making the face look smaller. For another, it hides the eyebrows which are a source of difficulty for girls around the world. Japanese tend to have bushy eyebrows so its easier to hide them than to pluck them to the perfect shape. And finally, when things trend in Japan, everyone copies and it stays a fad for a long long time. So what started in the 60s is going strong for 50+ years.
Recent years show this fad may be on its way out. More and more girls are parting their hair now - bangs might become the minority again.