Shape shifters and supernatural beings wage war in this fantasy-action manga. Though not what I would consider “ecchi”, it none the less provides ample amounts of well drawn nudity, as Seinen manga is known for doing.
Heaven’s Prison manga (first eight volumes, ongoing)
I haven’t read this in English, but going through the raw, I can tell you that things get quite graphic (the depictions of violence especially). FREEZING styled mutilations are quite commonplace in this one, and the nudity really only exists to up the shock value. Again, this is pretty standard in Seinen genre, though Heaven’s Prison takes it further than most.
Not every volume contains nudity, but when the manga goes there, it doesn’t skimp on the detail. I always love it when mangaka draw fat, plump nipples, so I’m a bit of a fan of the service in this series. Even if some of it is pretty weird.
I don’t think this manga will ever see an anime adaption, but I’d bet you that if it did, it would be non-nude. Seinen adaptations often remove the pointless nudity when going to animated form. Btooom! is a good example of that.
Heaven’s Prison is an ongoing manga. This installment represents the content from the eight volumes that are currently available.