Sansa and Arya Stark hated each other growing up. Both were manifestations of what they each dreaded becoming. With Sansa at Winterfell and Arya likely headed there as well, they are now poised for a highly likely and pivotal reunion, hinted at in the Game of Thrones Season 7 trailers:
Much has changed since #Arya and #Sansa last saw each other. Both have been thrust into a multitude of horrific and hopeless situations, yet they've not only survived, they've emerged stronger than ever before; Sansa as a politician and Arya as an assassin. There will now be newfound mutual respect, appreciation, and love, leading to fruitful action between these two sisters and survivors.
Arya Can Bridge The Tension Between Sansa And Jon
The reunion between Jon Snow and Sansa Stark and what followed was incredible and fascinating to behold. After years of suffering and torment, for the first time since season 1, Jon and Sansa had finally reconnected with family, and used that bond to move forward.
Love and compassion was always there, but trust only existed to a limited degree. Consequently, tension built as the season progressed, particularly as Jon refused to listen to Sansa's warnings about Ramsay, or alter his plan to take back Winterfell.
Furthermore, without Sansa contacting Littlefinger to bring the knights of the Vale, Ramsay and his allies would still hold Winterfell. Yet Jon is the one anointed King in the North while Sansa receives little real power or even credit. Jon and Sansa made their peace after retaking Winterfell but Jon's ascension to King in the North and Littlefinger's manipulations are already tearing at that peace.
Unlike Sansa, Arya was actually close with Jon in the days of growing up at Winterfell, bonded by their outcast statuses (Arya being a feisty tomboy rather than the polite lady she was supposed to be, and Jon as a bastard). Jon is the one who had Needle forged for Arya in the first place.
Capitalizing on the foundation of their relationship forged as children, Arya can bridge the tension between Sansa and Jon, helping both siblings learn to trust and support each other. Regardless of Jon's true parentage, they are all family raised by Ned and Catelyn Stark, and now the leaders of House Stark and the North.
Arya Will See Through Littlefinger
There's no shortage of complicated relationships in #GameofThrones, one of which is the Sansa-Littlefinger relationship. Sansa finally stood up to Littlefinger in a powerful, important scene that for the first time in the show explicitly spoke to the effects of sexual assault and the post-psychology of survivors.
However, this was not the end of their relationship. Thanks to the Vale army — needed to defeat Ramsay and his allies at Winterfell — and the ensuing alliance that formed between the North and the Vale, Littlefinger and Sansa are once again around each other.
Their relationship has changed but there's too much history and understanding between them to negate the relationship. Sansa knows what Littlefinger really is but also knows he can help fulfill her ambitions. In the season 6 finale and in the trailers for the upcoming season he speaks to her unparalleled survival and her right to rule the North. This will likely lead Sansa to trust Littlefinger more than she should.
Through her own identity but also through the skills she acquired from studying others as "No One," Arya will see right through Littlefinger. At the very least Arya can remember the last time she saw Littlefinger — he was meeting with Tywin Lannister, helping the Lannisters forge an alliance with the Tyrells to defeat not only Stannis Baratheon, but more importantly Robb Stark and the North.
Once Sansa can forsake all trust to Littlefinger, she can work with Arya to defeat Littlefinger for good. Using her political finesse, Sansa can distract and seduce Littlefinger with plans to seemingly actualize his dream of sitting on the Iron Throne with Sansa at his side. Meanwhile, Sansa and Arya can work to wrestle away Littlefinger's influence, taking his army and power from him, and eventually eliminating him for good. Eliminating Littlefinger will test everything they have but Sansa needs Arya in order to make it happen.
Sansa Can Help Arya Kill Cersei
Cersei is one of the few individuals remaining on Arya's kill list. For many reasons Cersei is more difficult to kill than the other individuals (Walder Frey, Meryn Trant, Polliver, etc.) Arya knows of Cersei's crimes against her family but she doesn't really know or understand the way Cersei operates.
Sansa does. During her years of captivity in King's Landing and specifically in the Red Keep, Sansa spent ample time around Cersei, watched her rise and fall all the way to Joffrey's death. Whether it's her passion for drinking wine, her boundless cruelty only capered by her children (all of whom are dead now), or how she uses her sexuality as a weapon, Sansa truly knows Cersei.
Arya cannot navigate King's Landing and the Red Keep and successfully kill Cersei without Sansa's knowledge, insights, or experience of the Queen, the city, and the castle. With all the time she lived in the Red Keep, Sansa may even be able to help Arya find a way to kill the Mountain.
Women Are The Real Power And Future Of Westeros
From Robert Baratheon to Tommen and the men featured in the War of Five Kings, kings have been dying left and right. Now Queen Cersei sits on the Iron Throne and Queen Daenerys lands at Dragonstone with an unparalleled array of forces. Other women like Brienne of Tarth, Yara Greyjoy, Olenna Tyrell, and Ellaria Sand currently operate in impressive positions as well.
Men have failed to rule Westeros and navigate the future. The women are the real power and future of Westeros now but it doesn't stop with the likes of Cersei and Daenerys. Together, an indomitable politician and assassin duo, Sansa and Arya can play integral roles in ruling the North and creating a future for Westeros despite the myriad threats.
What will be the most pivotal effects of an Arya-Sansa reunion in season 7?