Kyubey is a small, cat-like creature. It has white fur and four ears, one pair representing the average cat and the other similar to those of a rabbit's. It has red eyes and golden rings around its long ears. At the bottom of the ears, it appears that it is separated into three, along with a pink-white fade and three red ovals. These ears seem to be what turns the girls into magical girls, as seen when it makes Sayaka Miki's gem. It has a large tail and pointy ears, the inside of them being pinkish peach color. On its back is a hot pink egg-shaped oval that can flip open to remove Grief Seed fragments.
Despite appearing and sounding somewhat human, Kyubey is an Incubator and has no personal understanding of human emotion. Despite appearing as an individual, Kyubey and the rest of the Incubators do not seem to have a distinct sense of self. On the occasions where a Kyubey is killed, another will step out and continue to converse as if nothing had occurred.
The Incubators are an emotionless race, but seek to exploit the thermodynamics-violating emotions of the human race to produce energy and prevent the Heat Death of the Universe, the ultimate end of the universe itself. The fact that the system they use to harvest this power-- Magical girls and Witches-- would be considered horrendously evil by humans is inconsequential to the Incubators. They choose this method because it is the most expedient to their goals. No action they take is ultimately malicious, as they do not themselves experience or understand the emotions required to act in such a way. Everything about Kyubey, however, is implied to make it as appealing as possible to the Magical Girls, as well as emulating behaviors and 'emotions' for the same purpose. It is unknown if this body is the natural form of the Incubators, or simply a puppet used to interact with humanity.
This lack of understanding ultimately results in Kyubey being unable to predict or understand the actions of the Magical Girls or the results of those actions, despite them being obvious to the girls themselves.
Kyubey is a creature who makes contracts with young girls to turn them into "magical girls" so that they can fight witches. In this process, the girl makes a wish and Kyubey grants it, but in return, the girl's soul is put in a small gem, which is also the source of their magic. If destroyed, the magic will disappear and the girl will die. If it is corrupted with darkness from grief, the gem will turn into a grief seed and the girl will turn into a witch. This is the ultimate fate of all Magical girls.
Much like the rest of its race, Kyubey does not possess any human emotion. As seen in a later episode, Kyubey refers to magical girls' bodies as empty shells while explaining why Sayaka "died" when separated from her soul gem. This may also be why Homura Akemi got angry when Madoka Kaname threw it. Kyoko Sakura claims that it tricked and turned them into zombies, though it wasn't its intention. It believed that it was doing a good thing, seeing as it was convenient that they were invincible.
Despite its emotionless attitude, it apparently likes hot baths and human food, as seen in episode 2. It is also able to bleed, though it can reproduce its body and eat the old one. This body reproduction ability can be used whenever Kyubey's body is too damaged to be used or simply at an inconvenient state. (For example, is shown covered in bullet holes from being shot at.) It has an unlimited amount of these extra "bodies" that could be used, but it says that it would be more convenient to not use them so much.
- The spelling of Kyubey's name in Japanese is peculiar. It uses a mixture of hiragana and katakana, and the long u sound in "Kyu" is marked with a small u (ゥ) instead of a large u (ウ) or dash (ー). Both features are fairly uncommon and non-standard.
- Before the anime's first dark plot twist aired, head writer Gen Urobuchi said on his Twitter account that the "Kyu" in Kyubey's name comes from the English word "cute". This was a lie meant to further mislead fans into thinking that Madoka Magica is an innocent happy show. In a later episode, it was revealed that "Kyubey" is, in fact, short for "incubator".
- Kyubey's appearance and name share an affinity with Kyuubi, which are mythical Japanese foxes with nine tails. In folklore, Kyubey is known to possess men and have them do the Kyuubi's bidding, a trait identical to Kyubey's desire to collect energy from magical girls.