idk I never spend much attention thinking about Bran and Arya’s relationship because it’s actually pretty adorable? I mean you have
conflating opinions of who’s better at sword fighting:
She watched her little brother whack at Tommen. “I could do just as good as Bran,” she said. “He’s only seven. I’m nine.”
But that couldn’t be right. If the girl was Arya, the boy was Bran himself, and he had never worn his hair so long. And Arya never beat me playing swords, the way that girl is beating him.
snowball fights:
She remembered a summer’s snow in Winterfell when Arya and Bran had ambushed her as she emerged from the keep one morning. They’d each had a dozen snowballs to hand, and she’d had none.
Playing, Jon thought in astonishment, grown men playing like children, throwing snowballs the way Bran and Arya once did, and Robb and me before them.
caring about another’s feelings:
Arya bit her lip. “What will Bran do when he’s of age?” […] “He was going to be a knight,” Arya was saying now. “A knight of the Kingsguard. Can he still be a knight?”
She wondered how big Rickon had grown, and whether Bran was sad.
Robb was to marry one of their aunts, and Arya one of their uncles. “She never will,” Bran said, “not Arya,” […]
being reminded of them through other people:
Jojen was so solemn that Old Nan called him “little grandfather,” but Meera reminded Bran of his sister Arya. She wasn’t scared to get dirty, and she could run and fight and throw as good as a boy.
For a moment Bran thought it was his sister Arya … madly, for he knew his older sister was a thousand leagues away, or dead. And yet there she was, whirling, a scrawny thing, ragged, wild, her hair atangle. Tears filled Hodor’s eyes and froze there.
The girl was the older and taller of the two. Arya! Bran thought eagerly, as he watched her leap up onto a rock and cut at the boy. […] He saw no more of his father, nor the girl who looked like Arya.
fear over the other’s safety:
For a moment Arya forgot to breathe. Dead? Bran and Rickon, dead?
Might be it’s from Robb, come to say it wasn’t true about Bran and Rickon. She chewed on her lip, hoping. If I had wings I could fly back to Winterfell and see for myself.
protection from scary crypts:
That was when they heard the sound, low and deep and shivery. Baby Bran had clutched at Arya’s hand.
There may not be much, but what is there is pretty cute in my opinion.