As you can see in the title of this anime, there are many lines specific to “中二病” (ちゅうにびょう, Eighth Grader Syndrome). Chunibyo is a slang, which they believe that they possess supernatural powers and behave so. The word “中二病” is attached as “病” (びょう, disease) but it is not a real disease. Since it is close to the behavior of adolescent boys and girls in 2nd junior high school students (中学二年生, ちゅうがくにねんせい), it is called “中二病” (ちゅうにびょう, Eighth Grader Syndrome). Watching this anime helps your understandings about the concrete Chunibyo words well. From just the viewpoint of learning Japanese, this anime will not be good. (But, repeatedly, this is an outstanding anime!)
The main three characters all have the kanji “葉” (は, Leaf) in their name. The title: three leaves three colors is based on an idiom “Sansha-sanyo”, meaning everyone is unique.
The main theme song of this anime is very well-known for its amazingly fast lines and the associated dance performance. There are characters who have a distinctive way of speaking, such as geeky girls’ tone and lady-like tone.
There are elements like fantasy, including birds that speak human language, but there are many characters that speak natural ways that we hear on a daily basis. It is interesting to note that there are many character names related to mochi(rice cake).
The main characters use general Japanese, and a few use a unique phrase to emphasize their own character. This is a strong comedy anime, but they never talk in slang.