Artstyle really reminds me of Nozarashi Satoru, the hentai artist (it's "special" hentai; better not look unless you recognize the name (Trust me!)).
Sure there are deviations but, that might just be because of his assistants. On the whole Koppamu was either an assistant of said artist or it really is him; is my guess.
Sure there are deviations but, that might just be because of his assistants. On the whole Koppamu was either an assistant of said artist or it really is him; is my guess.