It's not always done poorly, but when it is it's annoying. If poorly written, they will speak in paragraph-long info dumps. Constantly refers to what kind of animal they are, or their non-human status is often milked for comedy.Sometimes is the source of the hero's power, or can become a walking deus ex machina.Usually able to talk and intelligent on a human level, though some may act more like animals.Is an animal, usually with supernatural powers and unusual characteristics.Associated with comedy, often breaks up dramatic tension with comedy.Homura Akemi from Puella Magi Madoka Magica resembles this character type superficially, but is also revealed to be a lot more complex the more you find out about her.
Satsuki from Kill La Kill shows that being this kind of character is not all it's cracked up to be, especially if you have a psychotic mom.Good Versions and Subversions of this Type: She's too honest and pure to do anything truly "outside the box." In other words, she's usually a Mary Sue and a Purity Sue type of character, too flawless to be genuine and human.
You know she's going to be heavily restricted by the bounds of propriety and honor, playing the "straight man" in contrast with wilder characters' antics. Most importantly, this kind of character is just rarely interesting. It also can be a cheap way to create drama: the totally average male protagonist (which I get to later) falling for the "dream girl" who is way out of his league. This trope glamorizes richness, making it seem like rich people are totally flawless, god-like beings. She seems like a very elegant and refined 30-something infiltrating the high school or middle school setting. She doesn't seem like her actual canonical age. Usually very pale-skinned, as per traditional Japanese beauty standards.Speaks very polite Japanese and has refined manners.Usually from a rich and/or well-connected family.Will either be the student council president or go to an elite school of some kind.(Or she will have a very precise, elegant hairstyle, like princess curls, pigtails, braids, etc.) Long, straight hair, usually black or purple, but may also be blonde or silver.Tall in stature, usually with an elegant silhouette.Everyone else looks like a dork around her.
She's an unrealistically swan-like presence in a school full of more realistically awkward teenagers. She is so perfect, you seriously wonder if she even poops. If you have a protagonist with a crush on senpai (an upperclassmen), the object of his desire is this girl. The Mary Sue Senpai (Also Known As: The Ojou-Sama)