Moonlight in Tokyo (2005)

Intellectually impaired he might be, Jun (Leon Lai) is only dumb but not silly. Abandoned by his family on a trip to Tokyo with only a few notes in his pocket, he thinks he has found his guardian angel when he bumps into a former classmate, Hoi (Chapman To). But Hoi is no angel at all. He is just a grifter on the run from yakuza loan sharks. When Yan (Yang Kuei-mei), the owner of an escort service, is convinced the ingenuous Jun will mark a perfect gigolo, Hoi decides to transform his pal into Tokyo's most sought-after Lothario in order to eke out a living and to pay his debts.