A Chao (チャオ? pronounced like "chow", in singular and plural form) is a lifeform from the Sonic the Hedgehog video game series. Their role in the games are to be raised by the player in mini-games, similar to many virtual pets. Chao are somewhat complex: they respond to stimuli, have moods, require food, and can be loving or fearful. The word Chao is a pun on Chaos, a word commonly used in the Sonic series and which is why the word remains unchanged when plural. The chao are the good friends of Cream the Rabbit and Tikal the Echidna.Making their first appearance in Sonic Adventure for the Dreamcast(both in the plot and in a Chao-raising aspect of the game), later inSonic Adventure 2, and further enhanced in Sonic Adventure 2: Battle, Sonic Advance and Sonic Adventure DX, Chao have recently come to be a large part of the Sonic the Hedgehogfranchise. Chao-raising and the main Sonic games tie together in a number of ways; items which you encounter in the main game can be used to raise your Chao, collected Rings can be used to buy things for them, and several unlockable features are related to Chao. During raising, Chao have statistics: Swimming, Flying, Running, Power, and Stamina, as well as a number of other things which aren't quite as obvious. These statistics can be raised through proper Chao raising, and will enable a Chao to do better in their competitions: Chao Racing and Chao Karate. Eggs other than those acquired in visiting a Chao Garden for the first time or mating are colored differently and reflect how the Chao will look. For example, a Gold Egg is solid gold in color and will hatch a solid Gold Chao. Ways of hatching them include snuggling the egg (the kindest way), throwing the egg at a wall (the Chao will obviously not like this), and of course, simply waiting for the egg to hatch on its own. When they hatch, they can be trained to have different attributes and emotional states. The Chao from Sonic Adventure 2,Sonic Adventure 2: Battle and Sonic Adventure DX can also favor "dark" and "hero" sides as well as the default "neutral" side which can lead to variations in visual evolution. Depending on the game, they take varying times to evolve. A Chao can also lose five minutes of its life by feeding it Heart Fruits, or gain ten minutes by eating Strong Fruits.
When evolving, they go into a cocoon state, which is white in the SA2 Dreamcast version of the game and blue for the GameCube version (both shaped like a chao's head). When they come out of this cocoon, (they will be in there for approximately 1 minute) the Chao is an adult, and can mate, which is curious for their apparent gender neutrality. After about 15-20 hours of time spent with the Chao, it will either transform into an egg again if it is treated kindly (into a pink cocoon - it will remember the player and all, but it will have only 10% of its old stats) or die if abused (gray cocoon).