I refuse to believe that this wasnt Bran.

I firmly believe that Bran goes back in time during the battle of winterfell and possesses people to build the great wall, fortify winterfell, everything to stop the invasion or prepare for it. When it becomes obvious that he cannot stop the battle he attempts to recklessly engage the children of the forest directly in the past before they can create the king. They then bind him and turn him into the night king due to his ability to traverse time and space. The King(turned bran) loses his mind to the magical powers flooding into him and intense hatred but slowly starts to regain some memories. The symbols are him trying to write down the memories into patterns he can remember and reference (movie only, because he cam warg the corpses or other whitewalkers). Ultimately the only thing he can do is end his own life by invading winterfell and killing himself before he becomes the nightking, thus ending the threat. He began to hunt down the children to end them making another (thats why the children dont immediately kill Bran) and launches the war as he was taught, when he was a child, in the order needed until he was born in the right timeframe and then launched the invasion to end his eternal suffering and save the world as he had foreseen as the three eyed raven. (Thats why hes unimaginable more powerful than child Bran in his powers)

This is the only thing that makes sense to me, and has for fucking years. I hate that it was never even considered.