I really don't care that he watches porn, I watch porn, we watch porn together. The only thing that bothers me is when I found out he has downloaded brother/sister hentai (anime porn) and ecchi manga (erotic graphic novels). He's assured me that he's not into /his/ sister and he just likes it because 'the characters are usually close in age'. That isn't true, usually one is older than the other and while I know it's not a pedophile thing it's hard to understand why. I told him it bothered me and he told me he doesn't usually like that, that he just 'over looks it' for the other content and that if it bothered me he would avoid it.
That was several months ago and today I was using google on his computer and autfil let me know he's actively seeking out stories/porn with sister/brother (Onii/Oneesan) relationships.
I don't really know what to think. We're both fairly kinky people (light bdsm, role playing, ect ect) but I don't get why he would want to watch boys have sex with their sisters.