Western animation and storytelling has come a long way in the last few years, but in many respects animation is still very much considered kids territory. A lot of anime is the same way but even a lot of basic shows tend to go beyond what Western shows will do and expose kids to simply because of cultural differences. When you go beyond the younger age set though and into older demographics, anime breaks quite a few boundaries that are a long way off for US animation studios. A number of them have been released in the US however and one of them even carried the Disney label.
1. Pom Poko
Considered one of the more outrageous titles from Studio Ghibli, Pom Poko was thought to be the one title that Disney would never release in America. While it plays big to the issues of environmentalism and urban sprawl, it centers on a group of raccoons that transform into humans to fight back. The twist? It's very graphic about the genitalia that the raccoons have when they're in a mode between pure animal and human. They're literally swinging around quite often, especially when the raccoons dance. It's certainly not something most parents would want to... expose their kids to.
While Hellsing deals with the usual round of vampires that populate a lot of shows, it crosses into religion pretty heavily as the Catholic Church is used extensively. The religious symbolism is big to begin with throughout with crosses abound, but when you have the Church sending out its own massively powered assassin that's quoting scripture and actively pursuing the goals set forth by the pope, it takes it to another level. What can top that? Heavy use of Nazi's with a group that's carrying on the goals of the past with extreme faithfulness. Swastika's abound and a belief in the thousand years of glory promised by the Fuhrer dominate the storyline.
3. Devilman Lady
A series created by Go Nagai, a man whose works have always broken boundaries, Devil Lady gives us a lead character that spends the bulk of the series naked and killing people as she copes with the transformations that she undergoes. Sexuality is fairly common in a lot of shows, but it's a rare show that places the lead in this kind of position with such regularity. The mixture of extreme violence, bloodshed and open sexuality has been a staple of anime for a long time and is almost unheard of when it comes to the vast majority of Western animation.
4. Sakura Diaries
Relationships in general don't show up in most shows in the West but an entire series revolving around a young woman doing her best to seduce her cousin that's moved in with her to go to college in the area? Incest abounds even as the young man does his best to win over a hot redhead from a different college. Filled with lots of overt sexuality, including the lead female pretending to be a prostitute upon first seeing her cousin after several years is still quite surprising even a decade after it first came out in Japan.
If there was ever a title that caused a lot of controversy in its release over here, and something that will likely never occur within animation originating in the US, it's Kite. Something of a near future title, it revolves around a teenage female assassin that's cold and brutal in what she does. There's enough unnerving material with the sexuality of the show considering her age, but the genesis of her role involves her being raped as a pre-teen in a brutal manner. It's an origin story you won't see in animation and even more rarely in the world of independent comics at best.