Bran Stark and the Night King share a mystical connection. While other characters on Game of Thrones are consumed by petty politics, Bran and the leader of the White Walkers tap into a deeper, darker magic. No one has been closer to the Night King than Bran Stark. No one has survived his proximity. No has one has even been touched by the Night King and lived to tell about it.
The “mark” that Bran received in season six has haunted him ever since. Like a tracking device, the blue handprint tattooed on his arm seems to give the Night King direct knowledge of Bran’s location. It’s what allowed him to enter the cave with Brynden Rivers and the Children of the Forest, and it's also what will propel the Night King south as he moves towards Winterfell.
This season, there were two crucial events that further hinted at the mysterious connection between Bran and the Night King. When the new Three-Eyed Raven warged into a flock of ravens, he was able to fly above the Army of the Dead and survey the scene. Though he got a good look at the encroaching horde, the Night King swiftly gazed at the birds and shattered Bran’s vision. The immediacy of this action caused Bran to jolt in his wheelchair, not the first or last time he had a pained reaction to the Night King’s presence.
In the penultimate episode of the season, we found the White Walkers armed to the hilt with newfound weapons and tools. The Night King conveniently had an armory of crystallized ice spears to kill Daenerys’ dragons, and when he succeeded, he ordered his minions to use a network of chains with links the size of footballs to hoist the beast out of its frozen grave. This level of preparation and prescience implies that the Night King has powers equal to, and potentially greater, than Bran Stark himself.
To be sure, while he is still mastering the tools of the Three-Eyed Raven trade, Bran is a rare breed. As told in A Song of Ice and Fire, “Only one man in a thousand is born a [warg]…and only one [warg] in a thousand can be a greenseer.” That makes Bran one in a million. He can't just greensee his way into the past, but he can also interact with it and warg into the players around him (as he proved with Hodor).
Though Bran may be a time traveling savant, he can’t outrun the Night King. However vindictive his pursuit may appear, it seems the Night King holds a more fundamental connection to Bran than anyone dare admit. As old (and recently revived) fan theories assert: Bran and the Night King could well be one in the same.
Wardrobe can be coincidental, but in Game of Thrones, no detail can be so readily discounted. Though there are stronger claims to assert that Bran Stark is the Night King, this striking visual is just icing on the cake. Additionally, in season 4, one of Bran's earliest greenseeing visions show the reflection of the Night King himself. How else could this be if Bran weren't either warging into (or living as) the Night King?
The genesis of this theory comes from Bran’s ability to interact with the past and his desire to change it. While many people assume that time travel in Game of Thrones operates on a closed loop, there is ample evidence to support that Bran has a unique influence on the past.
In A Dance With Dragons, he seeks out Ned Stark in the past and gets a response:
"Lord Eddard Stark sat upon a rock beside the deep black pool in the godswood, the pale roots of the heart tree twisting around him like an old man's gnarled arms. The greatsword Ice lay across Lord Eddard's lap, and he was cleaning the blade with an oilcloth. 'Winterfell,' Bran whispered. His father looked up. 'Who's there?' he asked."
In A Clash of Kings, Bran greensees and speaks to his brother years before the present:
The call came from behind him, softer than a whisper, but strong too. Can a shout be silent? He turned his head, searching for his brother, for a glimpse of a lean grey shape moving beneath the trees, but there was nothing, only...A weirwood…the weirwood had his brother’s face. Had his brother always had three eyes?
Not always, came the silent shout. Not before the crow.
On the show, we’ve seen Bran Stark's impact on Ned Stark at the Tower of Joy. A simple call of “father!” caused the young soldier to turn around and seek the source of the sound.
Brynden Rivers insisted that “the ink is dry, the past is already written,” but that may not be true. For every show of Bran’s ambition and desire to learn more, Brynden warned his apprentice to not get lost in the past: “It is beautiful beneath the sea; stay too long and you drown.” Similar statements are echoed by Jojen Reed when Bran would warg for hours on end into his direwolf, Summer. The fear that Bran could lose himself pervades almost every interaction with his mentors.