A Chiko is the next rank of Kitsune society, after Ashireiko in Japanese folklore. Kitsune belonging to this rank no longer look like ordinary, non-magical foxes, as they begin to sprout additional tails based on their age. This is the highest rank which wicked foxes, or Nogitsune, can achieve. Good foxes, or Zenko, can eventually advance to higher social ranks.
After one hundred years of age, a Kitsune can advance in rank from Ashireiko to Chiko. Most Chiko are between one hundred and five hundred years of age. For Kitsune who wish to continue to advance in society, this is a period of intense ascetic practice. As they grow in age and magical power, Chiko also begin to develop additional tails. The oldest and most powerful Chiko can have up to nine tails.
At around five hundred years of age, good Chiko may advance to the next rank of society and become Kiko. They shed their physical bodies and become spiritual entities. As for Nogitsune, Chiko is the highest rank they can ever achieve. No matter how many years they may live, how many tails they grow, or how powerful they become, they will never advance beyond this rank. Even the most famous and powerful nine-tailed Kitsune who became Tamamo no Mae only held the rank of Chiko.