Why Bran Stark is the target to kill of the Night King [Game of Thrones Final Season]?

When the Game of Thrones final season is over, it's obvious to us all that the real target of the Night King is not Jon Snow, nor Dany nor Cersei ... but a low-profile figure being Bran Stark. Why so?

Actually, the Night King does not care about Bran himself but his magical form being The Three-Eyed Raven - the keeper of the memories of man in the Westeros. So if he wants to destroy Westeros he must erase all trace of human kinds.

The Night King seems to be right about his pursuit of target since Bran Stark eventually and unexpectedly becomes the King of the Westeros. However, his plan comes to a failure when Arya suddenly appeared to kill him with the Vylarian steel dagger.

WATCH GAME OF THRONES SEASON 8 
EPISODE 3 -  THE LONG NIGHT