Be assured that this will be locked at the absolute first sign of flame, inappropriate pornographic discussion, etc, this will be locked, so prove that you all can be mature. Since this is a request for a religious opinion, don't twist the meaning of this sensitive subject, don't give it an interpretation that he didn't ask for, don't attack the advice given.
I'll be as basic as possible; the Bible outlaws all forms of sexual infidelity and pornography. Unfortunately; many people are cafeteria Christians and pick and choose their morality when the entire point of the faith is to have standards, to see things in pure black and white. Hentai is a form of pornography; though looked upon with less disdain and viewed with less guilt by people because they consider animated nudity to be less blackening than actual photographs. In fact, it's the same, because the motive in creating it is the same, the motive of the viewers is the same, and it's certainly not created as art; far different from, say, a nude statue of the Greeks and Romans, a Rococo image of cherubim or fantasy life, etc. Animated child pornography is legal; does that make it any less disturbing than the actual thing? Just because man's law may allow something, it does not give a faithful person a free ride to bypass God's law. Now, hentai that you accidentally stumble upon does not hurt you; the fault lies with the people that make it so easily visible; everyone who's ever searched for an anime picture has seen some on google or on a site that you think will be innocent before you actually go into it. I've pretty much seen any horrific image that you can mention, but it doesn't mean that I've enjoyed a second of it. I feel outrage and move on with my life; as accidents are not sin, they are merely what they are.