[Nyororin]

I have to say, that concert thing has to be the first forced separation I have heard of. I`m going to guess it was to fit the theme of the concert or the vision of the band.

In normal life there is no significant segregation. Toilets of course, along with changing rooms, public baths (but there are unsegregated ones too) and the like... There are female only train cars, but the rest of the cars aren`t male only so there is nothing stopping you from riding on them.
If you want to use the men`s restroom, and get into the men`s bath, etc - well, you`ll encounter problems. But otherwise I really haven`t heard of anything like that.