A Guardian Character (しゅごキャラ, Shugo Chara), also known as Guardian Chara is a tiny fairy born from the egg of a child's heart, called the Heart's Egg. The child's dreams and hopes is what preserves it. Sometimes, a strong emotion can trigger the egg to hatch into a Guardian Character in order to aid that person in becoming his or her would-be self and pursue his or her dreams.
However, if a Heart's Egg's owner is burdened by worries and doubts, the egg will turn into an X-Egg and eventually hatch into an evil and aggressive X-Character, and go on a rampage with its powers. Their owner is usually their first target. These characters are usually much stronger than their egg incarnations. The X-Characters are enemies in Shugo Chara!.
These creatures are invisible to normal people, and only owners of Guardian Characters and pure-hearted children can see them.
It is known that most people only have one Guardian Character, or sometimes two. However, there is an exception, as the protagonist Amu Hinamori has four Guardian Characters. Only two known characters have two guardian characters: singing idol Utau Hoshina (originally three) and Nadeshiko Fujisaki/Nagihiko Fujisaki. If two Guardian Characters share the same owner, the designs on their eggs will also share similarities, with difference in traits or colors.
It is explained in the manga that Guardian Characters generally only exist within the physical realm for the length of time their owner requires them for their personal growth. Of course, the events that allow this personal growth to occur not being certain to occur, how long exactly this takes would be completely unknown, even to the Chara themselves. In one case, that of Amu Hinamori, it was shown to even be possible for specific Characters of the same owner to disappear, despite others of that particular owner persisting to be present. However, that case would also be the only verified exception towards the "rule" of disappearance: After a day or so - long journey throughout both her own interior thoughts and the Road of Stars, Amu's Chara finally reappear towards her, although at first they sleep soundly within their Eggs, rather than their actual forms being seen towards the world.
It is verified by the actions of Tsukasa, who's Guardian Character had disappeared before the present events of the series, that those whose Chara have disappeared, can retain the ability to see the Chara of other people.
In order to be able to move freely, all Guardian Characters possess the ability to fly in the air.
Guardian Characters also possess a separate magic power of their own, depending on their representation. They can also sense the presence of fellow Guardian Characters, as well as X-Eggs, X-Characters and Heart's Eggs. They are invisible to those who do not have a Guardian Character of their own. The only ones who can see them are those who own a Guardian Character, those with a pure heart and those whose egg is well preserved, for example, Amu's little sister, Ami Hinamori. Guardian Characters can also communicate with animals.
A Guardian Character's main power is to use Character Change with its owner, which grants him or her limited special powers, and become the person the Guardian Character represents.
Character Change can only last for a short period of time, and while under the change, the owner will gain a certain feature that represents the change.
With some help from the magical Humpty Lock and Dumpty Key, the main Guardian Characters are able to merge with their owners and Character Transform into a more powerful character and use powers stronger than that of Character Change, as it increases the Guardian Character's power to 120%.