Our hero Guts is found as a baby laying in the mud under his dead mother who was hung by the neck from a tree. He is later rapped as a boy because his foster dad "sold" him for that purpose. (Kudos to Kentaro Miura for NOT drawing 19 pages of that.) Fast forward to the Golden Age Arc, Guts spends most of his time slicing people in half, disemboweling a hundred men in one setting. This is all following the dreams and ambitions of Griffith, a friend who once sold his body to some Lord who's either a pedophile or just into androgynous guys with long hair, for money to advance his own goals. After Guts decides to go off on his own, Griffith is tortured for a year having his tendons cut, his tongue cut out, and left to rot in a dungeon. One year later Guts and Casca get the band back together and rescue Griffith. Guts doesn't hold back slicing men in half and throwing them into a black pit as they make their escape. Then what many would call "a dick move" Griffith uses a Beherit to summon some demon lords and sacrifice almost everyone who ever cared for him in what is easily one of the bloodiest scenes in anime with his friends being torn apart, chewed up, and devoured by demons. There is also a 19 page raped scene involving Casca and Griffith as Guts watches him, helpless to do anything and has to cleave off his own arm to get free. Guts is then tackled by a demon and has one of his eyes torn out. Casca is then left in a regressed child-like state, while Guts searches the world for other demons to get his revenge on Griffith, and he's not afraid to have sex with them to do it! See Berserk Vol One, Page One for more details.
I could go on but I think I made my point. The thing that makes Berserk great is the quiet times of character development between the scenes of relentless violence that make this series one of the darkest fantasy series ever made. Not every episode or issue/volume is worth having an R rating but there's plenty in there that does.
That being said, I have seen anime series that focus more on the torture porn aspect. Blood C in particular comes to mind.
https://www.youtube.com/watch?v=wF-7x5op4iw