Akasen (赤線) is Japanese slang and a collective term which was used to identify districts in Japan where prostitution and the sex industry flourished until 1958, specifically during the period of January 1946 through March 1958.
Akasen means literally "red-line". The districts were the designated regions for state-regulated prostitution. Hundreds of government-sanctioned brothels and other adult entertainment parlors were operating in these districts, with the most popular being Yoshiwara in the Akasen region in Tokyo.
Another term Aosen (青線), literally "blue-line", was used for "non-permitted" or "non-legal" districts. In Tokyo, the area directly across the Sumida river from Yoshiwara (Tamanoi, now called Higashi Mukōjima) was a well-established aosen district; it features in some of Kafū Nagai's short stories.
Akasen is often compared directly with the term red-light district in the west. However, this does not explain why the counterpart "non-permitted districts" were called Aosen (blue-line). In practice, the Aosen and Akasen referred to the colors on municipal zoning maps that outlined brothel districts (Akasen) and "normal" entertainment districts (Aosen).
You may know me too well
From spending last night in that puddle
Kickin' my heart off in the trow
You tore a pity hole in your sock
You said "I will not join in your game"
Burnin' down whole houses of ice cream vendors
So please let them do whatever they may
For they have had every right
To make their living
To make their living
To make their living
To make their living
To make their living
You may know me too well
You may know me too well
You may know me too well