Manga8Mongrel Magazine, and Irish culture mag investigates tentacle hentai, with alook at manga-ka Toshio Maeda,

Our second contender for the octoperv crown is Toshio Maeda. Writing for an adult manga magazine in the early eighties – manga is, like, Pokemon people, and adult manga is Pokemon people having sex with schoolgirls – he realised that Japanese law forbade anatomically explicit pornographic drawings. In his own, semitranslated words: “At that time, 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.” In other words, having discovered that he couldn’t draw sex with willies, it occurred to him to draw sex with large, multi-tentacled animals, and young girls.

Maeda is best known for Urotsukidoji, which, apparently, CPM published for a while.