Usa is the leader of the Chi Clan. He is the father of China, Ojinaga and Saratoga. He, along with his wife, Song-kou, use the family temple as a dojo for training young warriors to battle and also teaching young people martial art techniques.
Aysa Mihos is technically a part of the Beta Clan orginally, but her immediate family is split between Chi Clan and the Beta Clan. Because Aysa's aunt Song-Kou married into the Chi Clan, Aysa decided to disown her father and join their clan instead. She was basically raised by her aunt in this clan because her father, Dr. Mihos, turned evil and her mother passed away.
China is the eldest son of Usa and a prize for their family. They enroll him in the Tau Tournament year after year in hopes that he would defeat the Tau Clan's eldest daughter, Aikido. Much like the Borealis-Australis feud, the Chi and Tau Clan's have been feuding for centuries, but they reconcile their differences later on in Volume 5.