Fou is the guardian deity of the Black Order's Asia Branch, sealed by Bak's great-grandfather. Although she is not human, she often takes on a humanoid form to talk with others. Fou found Allen's body after Tyki Mikk's attack and took him to the Asia Branch headquarters. She has a "tough-love" attitude, particularly towards Allen. While she was training Allen in an attempt to bring back his Innocence, she would attack without mercy with the hope that he would activate his left arm. When Allen was feeling down, she would appear in front of him as someone else (eg:Lou Fa (this way she could show her soft side without Allen knowing).

She shares a strong bond with Bak even though she loves to tease him. She can manipulate her form in order to change her hands into axe-like weapons or to copy someone's appearance. She is also capable of communicating telepathically with others. The Headquarters of the Asia Branch is protected by a very strong barrier created by Fou (who is the "entrance" of the barrier). Under her tough shell Fou is a very caring individual and is quite willing to give up her life for the sake of those she loves. She took Allen's form to face the level 3 Akuma, in order to buy the real Allen time to escape. Just before they began to fight, she said to herself "Bye bye, Bak." She was hurt badly in the battle, but after Allen defeated the Akuma she is shown to be recovering.

Source: Wikipedia