Fang Yu is a member of the Fang Clan. She is one of the recurring characters in the novel.
Meng Hao encountered her in Choumen Tai's mental realm for the first time. She used incredibly powerful fist strikes to attack him. But after seeing the mark of his bloodline diverts her attacks. This causes Meng Hao to think she's crazy. The second time Fang Yu encounters Meng Hao is in the ruins of the Demon Immortal Sect. This time around she helps Meng Hao a lot.
She was revealed to be Meng Hao's older sister. It was secretly arranged that she be a sect disciple of the Church of the Immortal Emperor after breaking through the Immortal Realm. Thus, not even Fang Clan members were aware that she became a disciple of this sect. She then met Sun Hai there, a Chosen of the above-mentioned sect, who fell in love with her.