A Chao (pronounced IPA-tʃaʊ', or "chow", singular and plural form Chao) 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, responding to stimuli, they have moods, they require food, and they can be loving or fearful. The word chao is a pun on chaos, a word commonly used in the Sonic series.
Making their first appearance in Sonic Adventure for the Dreamcast (both in the plot and in a Chao-raising aspect of the game), later in Sonic 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 Hedgehog franchise. 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.
Chao have appeared in plenty of Sonic the Hedgehog games, including Sonic Adventure, Sonic Adventure 2, Sonic Adventure 2: Battle, Sonic Advance, Sonic Advance 2, Sonic Advance 3, Sonic Pinball Party, Sonic Shuffle, Sonic Adventure DX: Director's Cut, Sonic Heroes, Sega Superstars,Sonic Rivals 2,Sonic Chronicles: The Dark Brotherhood, A mission in the 360 & PS3 Versions of Sonic Unleashed and Shadow the Hedgehog. Earlier forms of the technology behind them, were also in NiGHTS Into Dreams with the Nightopians (the A-lives).A Chao is also a merchant in a few games.Sonic Riders for example.
Chao start life in an egg state. The eggs of a common Chao are white with a yellow splotch on the top and blue freckles. 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, while a Morning Glory Egg will hatch a Flower 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).
After one Chao year has passed (about 2-3 hours for GameCube versions, 1 hour for Dreamcast) Chao create a cocoon and evolve into a more mature form. It will mature into a form that features both its highest leveled stat (running, swimming, power, flying or normal) and its alignment. During this evolution, a Chao raises one grade up in the level of its type, e.g. a swimming Chao who has a grade 'B' in swimming becomes an 'A'.
Alignment is determined by how the Chao was treated before its evolution, and the three alignments are 'Dark', 'Hero', and 'Neutral'. There are three Hero characters (Sonic, Knuckles, and Tails) and three Dark characters (Shadow, Rouge, and Dr. Eggman) in Sonic Adventure 2. Petting, holding, or cuddling a Chao with a character makes the Chao favor the character's alignment. Attacking, throwing, stepping on a Chao, or taking its food while it is eating makes it favor the opposite alignment of the character. Every three times that a heart appears above a Chao's head and replaces the standard emotion, the Chao darkens or lightens a shade, a darker shade coinciding with becoming a Dark Chao, and vice versa. A Chao's physical appearance is the chief indicator in understanding the alignment of a Chao. Dark Chao have leathery wings and a devil's tail, and are colored black, brown, and red with a small spike ball on its head.It also has a symbol on it's chest similar to Knuckles'. Hero Chao have feathery wings, a split tail, and a small halo on its head. They are colored white, blue, and gold. Neutral chao are created by balancing contact by both Hero and Dark characters, or not paying attention to them. They are able to look like a lot of different characters. In Sonic Adventure DX, due to only heroic characters being playable, the Chao instead become Hero or Dark depending on the fruits it is given.
Chao will evolve a second time after 4-5 Chao years. However, the Chao won't go into a cocoon, and the changes are sometimes very subtle. A Chao will 'evolve' depending on which stat is the highest at the moment. However, it won't change its primary type. You can also change a Chao that has already gone through its second evolution. For example, if you had a Dark/Fly Chao and gave a lot of purple Chaos Drives/Animals it would become a Dark/Fly/Fly Chao. However, if you then gave it Red Chaos Drives/Animals, its appearance would change again, and it would become a Dark/Fly/Power Chao.
After four to five Chao years have passed, the Chao will either transform or die. If the Chao has lived a happy life, it will be surrounded by a pink cocoon, and will be reborn as an egg and hatch as a Baby Chao. However, a Chao that has been ignored and abused during its lifetime will surround itself with a gray cocoon, that will leave nothing behind after vanishing.
Besides the normal evolutions, a special Chao called the 'Chaos Chao' can be created. This can be done once the selected Chao has transformed two times. During that third cycle of its life, if it is given one of each animal in the game, but given NO chaos drives, it will become a Chaos Chao. Besides looking different than a normal Chao, the Chaos Chao has an unending lifespan, except a death through extreme character abuse (not proven). In Sonic Adventure 2, there's also the 'Hero Chaos Chao', also known as the "Angel Chaos Chao", and 'Dark Chaos Chao', also known as the "Devil Chao", along with the normal 'Neutral Chaos Chao, also known as the Light Chaos Chao' (shaped like Chaos) from the original Sonic Adventure. Evolution works in the same manner, except you give them one animal from either the Hero or Dark characters respectively, and that no Chaos Drives must be given to them. Along with their apparent invincibility, Chaos Chao also lack the ability to reproduce. They are probably the most difficult chao to create the best way to make sure you've gotton all animals is to make a checklist.
The DS chao do not evolve. They learn to be used as weapons.
After evolving, Chao gain the ability to reproduce. Chao have no gender and therefore can breed with any other adult Chao. Chao are in mating season when they sit down happily and are surrounded by a circle of flowers. While this happens twice naturally, it can also be achieved by purchasing 'Heart Fruit' from the Black Market in Sonic Adventure 2 and giving it to an adult Chao). Placing another Chao inside the circle may result in breeding. Most Chao are compatible, a Hero Chao can breed with a Dark Chao, and vice versa. It is believed that, to at least some degree, statistics and other characteristics are inherited. As mentioned above, Chaos Chao cannot breed.
By giving a Chao a 'small animal', it will acquire some of the animal's characteristics. Besides a physical change to the Chao, this will also modify the Chao's stats based on the type of animal given. There are five types of animals in Sonic Adventure and 7 in Sonic Adventure 2. They consist of Running (Green), Power (Red), Swimming (Yellow) and Flying (Purple). The fifth color, Blue, is a fairly even mixture of some or all of the other classes. The two additional types featured in Sonic Adventure 2 are Ghost (Black) and Imaginary (Gold), sometimes called Legendary. The Ghost animals raise Intelligence and Imaginary animals raise luck (These two stats cannot be seen). The Ghost and Imaginary animals give better than average stat increases and do not lower any stats.
In Sonic Adventure 2, 'Chaos Drives' appear. Chaos Drives are items that pop out of machines created by the military organization G.U.N. when they are destroyed. These, like the small animals, also raise your Chao's stats. These are only in Sonic Adventure 2 and the GameCube adaptation. Like the small animals, the different colors each raise a certain stat. Yellow raises swim, purple raises fly, green raises run, and red raises power.
However, neither animals nor Chaos Drives can raise a Chao's stamina, only food can. Also, a certain fruit called the Chao Fruit raises all stats, including Stamina, when it is given to a Chao.
In certain games like Sonic Adventure 2 Battle (after the evolution into a Hero, Neutral, or Dark Chao), Chao go into an either pink or gray cocoon at the end of their lifespan. The pink cocoon means they're reincarnating, and the gray means they're going to die. Chaos Chao (all types) are immortal; thus, they will never enter into a cocoon once formed. A reincarnated Chao keeps all of its letter grades from its previous life as well as its skills, tools, awards, and even intelligence. Its stat levels will reset to 1, but reincarnated Chao also retain 10% of their stats totals prior to death. With enough time and effort, this enables the player to eventually maximize all stats if they're raised to lv. 99 in each lifetime.
A Chao will also appear in the Super Jump Punch! comics and Super Mario: The Mystery of HeartGold and SoulSilver special.