So anime is a pretty big topic. There is action, adventure, comedy, horror and harem, which is just someone with many love interests. But what makes an anime? That is a question that every that watches anime usually has. But there are usually only three things that make an anime very interesting to watch and enjoy. These three things are characters, story telling and the overall mood of the anime.
Characters are vital in pretty much anything. There is the main character, the person opposing the main character, the friends for both, random individuals, and people who have very different personalities. These characters make the anime show they are in be that anime. When you have no characters in a plot to the anime, the story becomes stupid and sour. It becomes nothing more than an ordinary story.
The next thing that makes an anime is story telling. Now, this is sometimes broken by anime because it jumps around, but this one is an alright rule. But the anime should have a story following the main character or follow a certain person every episode. This gives the viewer either a chance to see how the main character will overcome his or her arch enemy or even just show different horrors that take place. An example of the third on is Blood C. Please do not watch this if you are not a fan of horror anime. But anyways story telling is great for the anime's main purpose so it has to be in there sometimes.
So the overall mood of the anime does not make an anime's story or makes the characters. It makes the whole thing very original. Take Blood C for instance. It defines the horror genre in my opinion and the overall mood is especially dark and focuses more on monsters, blood, and random things more than anything else. This makes this anime very popular but again do not watch this anime unless you love this genre and can handle it.
So these three things make anime what it is. But these things do have to adapt to the changes just as people do. So when it adapts it still follows those three rules and can sometimes make something eve better than before.
