She is demanding, demeaning & constantly nagging her boyfriend, American Boyfriend. The two fight constantly, often physically assaulting each other, usually including her being strangled. It is revealed she has a shrimp allergy, which causes her to throw up. She also claims that she can't read English & speaks in a stereotypical Japanese-English accent (often stylized as Engrish).
In A Day at the Park, she behaves typically to her boyfriend in front of his boss. Jürgen mistakes her for a man & apologizes to the couple for making "so many jokes". Later, she hustles Vishalam Rangan for hush money, commenting on her fake identity. She walks away from Rangan with her Von Clubs card, still talking in a Japanese accent before her voice deepens & (s)he call Rangan a sucker.
It is possible for Asian Girlfriend to be a persona that they inhabit. Their motives have otherwise not been revealed, but money could be involved.