Mu Yubai is the oldest son of Mu Feiyan, the head of the Mu Guardian Family, making him the Young Patriarch of the Mu Family. After Yun Che started to heal Yun Qinghong and Mu Yurous injuries he was very persistent on becoming sworn brothers with him not knowing that all that time that he was his nephew.
He looked to be roughly around thirty years old. He was tall and broad, and his beard filled his face. He seemed to be a person who was unconcerned with his appearance, but his eyes were as fierce as a wild tiger’s; they were forcefully imposing. 
Mu Yubai has a very loyal and straightforward personality which can be seen when he tries to take Yun Che, who was a complete stranger until recently, his sworn brother for healing Yun Qinghong and Mu Yurou.