It's been a long time since I watched anime last. I just haven't found it interesting lately.
That was, until I found out about Koi Kaze, and anime that tackles the subject of a brother and a sister falling in love.

Now, the brother/sister attraction thing is nothing new in anime. Lots of pandering, low-brow anime use it as a topic, but what was different with Koi Kaze is that it did it entirely without pandering. No fanservice what so ever, and no attempts at sexualizing it in any way. Just to explore the situation of a brother and a sister falling in love, and the troubles it causes.
Straight-faced, serious and mature.

And I'm really fascinated by that, and I wonder if there are more anime that does this. That is, tackling controversial and/or taboo subjects without being juvenile, pandering, sexualizing or glorifying the subject matter. Anime that takes themselves and their subject matter seriously.
Does anyone know of any such anime?

Boku no pico.

Elfen Lied. Yes, it is a very bloody anime, and yes, it is about a mutation in the human genes that created the Diclonius, but it is a very serious anime about the darker sides of human nature as well, without doing pandering, fanservice or sexualization. Thought the love part in it isn't between a sister and brother, it is between cousins. If you can get past how violent that it is at times, it's a very engrossing anime with a beautifully and interestingly done story that sucks you in more than the science fiction part of it.

*Though the love part, is how that's supposed to read. Darn typos. >.>

No fanservice?
Did we watch the same anime?
If I remember correctly I believe that both the anime and manga contain quite a bit of fanservice.
Not that Elfen Lied isn't great, because it is, but the fanservice bits in it just annoy me.

It's hard to find thought provoking anime about risque subjects that uses little fan service. I certainly enjoy it though when I come across one, I hadn't heard about Koi Kaze before so I'll definitely be checking it out now.

Very interesting topic! I don't know many anime like that though I have seen Koi Kaze and loved it's handling of such a taboo topic.

What about Puella Magi Madoka Magica? It is a deep, dark anime that explores the dark side of wishes and contracts in a way. And for all its cute-art, it is very mature.

Revolutionary Girl Utena/Adolescence of Utena feature heavily taboo topic in a metaphysical/symbolic/allegorical way, while under guise of a warped version of "growing up" and reaching the "adult world".

I want to say something about the Chobits manga (NOT the anime adaptation) because even though it DOES include fanservice and it is ecchi, it still asks plenty of hard-to-answer questions. Like does artificial intelligence have free will/deserve love? Is a relationship between a human and a persecom/robot fine or wrong? What is love, and is it truly limitless or does it come with boundaries when the relationship is not shared between a human and another human(s)?

Serial Experiments Lain is mature, dark, classic series that focuses on the modern world's relationship with technology and both the good and bad side of things. Highly surreal and allegorical. Not for people who want something plainly stated.

Then there's Now and Then, Here and There which is such a heartbreaking and beautiful series that no one knows about sadly. It is about war, and the consequences of it. It talks and features things like child soldiers, rape, loss of innocence, loss of humanity among other touchy topics.

I actually loled, not because it was funny, but because of how irrelevant it was for you to have quoted me.

I know, I know. But I couldn't resist putting a shout-out of another horrible series out there.

Shhh, you're not meant to say that, we're trying to ruin this guy's life forever.

Thought provoking/mature anime hmm...

Natsuyuki Rendezvous, very mature approach to the whole love/romance anime
Angels Beats
Bakemonogatari/Nisemonogatari

Those are the 3 that immediately come to mind

AnoHana deals with very mature subject matter in a great way. It doesn't deal in something taboo as it is controversial and heart-wrenching. The first episode would be enough to tell you if it's what you're looking for.

code geass

http://www.crunchyroll.com/hourou-musuko-wandering-son