Sometimes we tend to complicate things when in reality things can be explained in very simple terms. 
Our original "fathers" did sin against God. Therefore we all are "broken" nevertheless have the freedom to choose between doing good or choose to do evil ( complete freedom which equates to perfect love).  
This is what the Angel refers to at the end of the movie.
Angels and demons are spiritual beings although it is believed they do take physical form though it is very rare. Demons are also spiritual beings and they can take posession of people's will and body -if- invited in.(Witchcraft and sorcery).
The world is the scene of an epic battle between good and evil. People invite evil or choose good every day.  Faith answers to God and doubt and fear to the Devil. The Angel fights off the Devil and demons all throughout the movie. 
The japanese shaman is the devil's subject. He chooses people, prepares the scene, performs the "exorcisms" and when people are tested, they choose doubt and fear and then they are killed or they survive the attacks according to their choice based on freewill. Then the devil's subject and demon moves on to get more souls. 
At the end of the movie, we see and understand the Devil and evil are real indeed. Nevertheless, he is unable to take anyone if people hold strong to Faith and what cannot be seen. True and pure love -fidelity to the most sacred covenant between people has a special place at the end of the movie when we see the dad and daughter come together in complete happiness and union.