Light In the dark (Shugo Chara)

Guardian Chara 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 rampage with its powers.