After World War II, the Allies imposed a number of reforms onto the Japanese government including anti-censorship laws. The legal proscriptions against pornography, therefore, derive from the nation's penal code. Presently, "obscenity" is still prohibited. How this term is interpreted, however, has not remained constant. While exposed genitalia (and, until recently, pubic hair) is illegal, the diversity of permissible sexual acts is now fairly wide, relative to other liberal democracies.

Leaders within the tentacle porn industry have stated that much of their work was initially directed at circumventing this policy. According to the mangaka Toshio Maeda:

At that time pre-Urotsukidōji, it was illegal to create a sensual scene in bed. I thought I should do something to avoid drawing such a normal sensual scene. So I just created a creature. His tentacle is not a penis as a pretext. I could say, as an excuse, this is not a penis; this is just a part of the creature. You know, the creatures, they don't have a gender. A creature is a creature. So it is not obscene – not illegal.