Kunio just got a new girlfriend, Mayu. What Mayu doesn't know yet, is that Kunio has a hobby of taking pictures of his girlfriends during sex and send them to amateur porn magazines. When she discovers that fact, it turns her even more on.

Is it possible to learn Japanese through anime? What would a total beginner need to understand anime conversations?

Well, you ask two different questions there...
one is about learning Japanese via Anime, the other is about learning Japanese for Anime.
I will try to answer both, but it makes for a long post.
So bear with me. As for learning via Anime: just like Tarek, I'm one of those humans who would have experienced that exact effect if it were possible.
I have been constantly watching anime since my teen years, and started watching it in subtitled form more than 12 years ago. So, was I able to learn Japanese only via anime? No. But did watching anime do wonders for my Japanese? Hell, yeah! What watching anime can NOT do for you: - It does not provide you with grammatical information.
Now, Japanese grammar is nothing to be scared of (far easier to learn than German for example), but it is very different from Western language grammar.
There is no chance that you would be able to spot and understand the underlying grammatical structures just from listening to anime. - It does not provide you with sufficient verb vocabulary.
Not because anime uses less verbs, but because Japanese verbs are notoriously hard to spot and analyze in audio form without having a firm grasp on the grammar first.
This continues even for some time after you have gained a basic understanding of Japanese.
Only later will you become able to mentally extract/gain new verbs from mere audio content.
Until then, you need text for this. - It does not provide you with the full range of polite language you learn in a J.
While the Japanese used in anime is indeed grammatically correct and valid, it has its quirks.
First of all, it usually skips a lot of the politeness levels present in common Japanese (because that makes it easier to listen to, even for Japanese).
So, people will definitely understand you, but you will probably sound more rude than you intend to.
That being said, Gaijin who can speak Japanese are so rare that you will receive a lot of leeway there.
Meaning that people usually won't mind unless you speak in a business or formal context. - It does not (necessarily) provide you with a manner of speaking that is fully appropriate for your age and gender.
Anime casts, on average, are predominantly female.
Also, female Seiyuu tend speak more clearly than male ones do.
As a result, the Japanese you pick up can be inadvertently tinged with some female phrases and mannerisms.
However, this is a luxury problem in my eyes.
Once you have reached the point that you are far enough into Japanese to worry about the nuances of your language, you will most likely be capable of switching to a male idiom. What watching anime CAN do for you: - You will acquire the "speech melody" and pronounciation of Japanese syllables.
Once you start speaking, you will instinctively know how to pronounce words and how "good Japanese" should sound.
Anime does this far better than any course could ever teach you. - You will acquire a lot of nouns and phrases.
Picking up phrases is extremely easy via anime, and you will even always get a situational exampe for when to use them, too.
Similar things go for nouns.
They are fully static, and thus pretty easy to spot and reuse. - Anime will provide an emotional backdrop facilitating your learning process.
Imagine sitting down with a vocabulary book.
Every other entry will remind you of a scene, character or series you liked.
Granted, this will not work for all words, but for a lot of them.
At the same time, Anime ensures that you keep a positive attitude towards the language itself.
And learning a language is miles faster/easier if you feel something for it, trust me on that.
(The reason for that is hard brain chemistry, but I digress.) - You will acquire a lot of cultural context.
Let's face it, seen from a Western viewpoint Japan is odd.
Mind, not in the "weird and crazy" sense, but simply the fact that many cultural and social mannerisms are particular to Japan and require explanation if you never saw them before.
This starts with putting off your shoes as you enter a house and ends with superstitious people not cutting their fingernails at night.
Learning all that by asking or reading up is flat out impossible.
Anime however will serve this stuff to you every day on a silver plate, nicely marked with humor/exaggeration for you to notice.
I can not possibly overemphasize how extremely helpful this turns out later. What I recommend you to do: First, watch anime subtitled for a couple of years.
During that time, learn reading Hiragana and Katakana on the side.
Yes, it's tedious, but it will come in handy in countless places later.
For example, once you know which syllables Japanese has (and which it does not have), you can grasp and spot words better than before.
If you look for the minimal path, don't bother with learning to write Hiragana/Katakana at that point, and especially stay away from Kanji. After that, join a Japanese classroom course.
With the Hiragana/Katakana and anime under your belt, you will be miles ahead of your class right off the bat.
When I did so, I was basically breezing through the chapters, to the point of having to restrain myself to not bother the others.
You will find that tons of things others struggle with will come just natural to you.
Stick around long enough to get an introduction to (and material on) all grammar except for Keigo and Classic Japanese.
Since you have your headstart, you can even consider choosing one or two several-weeks crash courses rather than ones lasting months or years.
I'm definitely not a language genius, but I did so, and never regretted it. Keep watching Anime.
Watch anime of the genre that you enjoy most (chances are it will be easiest for you to understand).
Strictly avoid pure comedy series though, the dialogue is usually too fast and convoluted for beginners.
If you are using .mkv files, you can start by switching off subtitles now and then.
Note that you won't be able to understand everything right away, even after the course.
When I returned from my course, I could understand about 40% of the dialogue in my favourite genres (romance/fanservice/drama).
Over some months, I got to 80%.
Years later, I'm now at 95%. Last, travel to Japan.
It will ground your language experience and teach you the subtle differences between anime Japanese and common Japanese. Congratulations, you know Japanese.
=) = = = = =TL;DR: = = = = = If you are asking if it is possible to learn Japanese only through anime, then sadly the answer is "no dice".
You need at least one Japanese course as well.
But, once you decide to join such a course, having watched anime for some years will give you an amazing headstart over everyone else, as well as constantly boost your progress during learning.