Please don't actually link some hentai, or at least spoiler (and leave a warning) for it. I'm legitimately curious about this.
So a friend of mine linked me this manga called Seishokuki. Without giving too much away it's basically about a high school girl with a huge libido who has to fight stuffed animal aliens to stop them from taking over the world. It's a ludicrous idea, but pretty damn lewd if you're into that kind of thing.
What is really odd though, is that she constantly gets raped by the stuffed animal's tentacle tongues (it makes sense in context sort of) and it shows the whole thing. No discretion shot, they just censor the naughty bits. This isn't a one-off thing, it happens throughout the whole series.
The thing is, I've seen hentai that is much less explicit (since all porn in Japan requires censoring) where it's just a loving couple who have sex for like a few pages. Yet this series is considered "mature" (as in young adult like Great Teacher Onizuka or High School of the Dead) while the latter will be considered porn. What exactly is the difference? Don't say that sex isn't the main focus, because that definitely is the main focus of Seishokuki while I've read hentai that have a huge focus on story to the point that the sex is secondary.
If a story like the one I posted can be considered just "ecchi" then what exactly makes something hentai?
Mod Edit: NSFW links removed – Crimson