I read a doujinshi on hentaifox a while back, in which two girls tortured and trained a boy to cum on command. Then later he is let go, has a normal-ish life until he meets the girls on the sidewalk, they say the code word, he cums uncontrollably right then and there and get hummiliated inffont of everybody.
Cant really remember anymore details, the girls could have been demons/succubus, but not sure about it.