Instructions
Raise a Chao from birth to death. When it's a baby, give it either chaos drives or animals, because it needs these to evolve into an adult. Once your Chao grows into an adult, treat it well by visiting it often and giving it gifts. When it reaches approximately age five, it will form a cocoon, fading into death. However, if it liked you, it will leave behind an egg.
Care for the Chao through its second incarnation. When it emerges from its egg, it will look similar to other baby Chao, but it will retain its name and its relationship with you. Maintain that relationship through its second death so that it will reincarnate into a third life.
Give the Chao one--and only one--of each animal. There are 21 animals. Once you do this, you need to decide whether you want a Light, Angel or Devil Chao. These are immortal.
Visit the Black Market. Buy either a chao fruit (for a Light Chao), a hero fruit (for an Angel Chao) or a dark fruit (for a Devil Chao). Feed the fruit to your Chao, and it will become one of these three rare Chaos. As an alternative to purchasing the fruit, you can raise the Chao to have each affinity. For the Light Chao, raise it neutrally, caring for it equally with hero characters (Knuckles, Sonic or Tails) and with dark characters (Shadow, Rouge or Eggman). Raise the Angel Chao with only hero characters or the Devil Chao with only dark characters.