Warning: SPOILERS ahead for the Game of Thrones season 7 finale
Cersei and Jaime were born minutes apart, but the Game of Thrones seventh season finale has pitted them against each other. It’s no longer enough for him to shrug his shoulders and, “the things we do for love.” To continue following her lead, Jaime demands more of his sister. Though he dutifully acknowledged that the reign of House Lannister is now secondary to the defeat of the White Walkers, the Mad Queen reneged on her agreement to support Daenerys Targaryen and Jon Snow. While Jaime is no stranger to his sister’s machinations, this was a bridge too far. As a result, he left King’s Landing and his pregnant sister behind.
This is a major moment for Jaime Lannister. Throughout the series, we have watched him grow from a sniveling sister-lover to a humbled and empathetic man. Though he has come close to parting ways with Cersei on multiple occasions, he continually crawled back to her manipulative world, a slave to her both physically and emotionally.
At the end of season six, however, we saw a glimpse of hope. When Cersei took the Iron Throne after detonating the Sept of Baelor, Jaime looked on at the proceedings with palpable mistrust. However much he has loved his sister, he has always known her greatest weakness: the lust for pure, unmitigated power. So strong is this call to glory that she refused to even talk about the suicide of their son, Tommen, instead looking ahead to their “thousand year-reign.”
In season seven, Cersei has had to sell Jaime on her new vision. While previous episodes have shown him throwing himself at her, his recent restraint has driven Cersei to control her brother. To be sure, her newfound pregnancy embodies her desire to keep Jaime by her side.
When she promised to send her men to the north, the safety of the Seven Kingdoms seemed promising. There was peace in the Dragonpit, at least the appearance of it. When Cersei told Jaime of her covert deal with Euron Greyjoy, however, he realized that the other leaders had been played. Like Tywin Lannister before her, Cersei hedged her bets that Jon and Dany would use their dragons and men to take down the White Walkers, weaken their army, and allow the forces of King’s Landing to sweep them over at war’s end.
It’s the exact strategy Tywin employed against King Aerys during Robert’s Rebellion. The Targaryen army had been dealt a vicious blow at The Battle of the Trident, forcing Aerys to open the gates of King’s Landing to his Hand, Tywin. Though he feigned support, Tywin ordered his men to ransack the city, crush the military, and carry out the coup d’etat.
While we haven’t learned the full extent of Cersei’s plan with Euron and the Golden Company of Essos, it’s clear they mean to employ as many sellswords as possible to crush the latest Targaryen alliance.
Jaime will not be fighting for his sister any longer. He despises Euron Greyjoy and will have no part in their unholy alliance. In a sense, he just broke up with Cersei for the first time in his adult life. By severing his relationship with her and literally leaving King’s Landing, he has set out on a soul-searching journey akin to his days of wandering and imprisonment beside Brienne of Tarth.
The Kingslayer’s character arc is one of the broadest and most effective in all of the show. He has yet to reach his peak, but fleeing from Cersei’s crooked reign is the first step towards the life he deserves. Stripped of his constraining Lannister armor and identity, Jaime is free to fight for whomever he chooses.
It won't be an automatic assimilation with the northern leaders, however, seeing as Jaime has bad blood with the Stark and Targaryen families. He personally assassinated Daenerys’ father and Aegon’s grandfather, though both Targaryens would hopefully agree that he did the Seven Kingdoms a favor.
While a few charged words may be had between Jaime, Jon, and Dany, there’s no doubt that the Mother of Dragons and the King in the North will be glad to have the Kingslayer fight on their behalf. On the other hand, Jaime may be the one to dish some epithets at Dany, considering she personally roasted his men to ash in the fields around the Blackwater Rush.
Unfortunately, Jaime will no longer have the Lannister army following his command, and it remains to be seen how he will get his hands on one of Qyburn’s deadly Scorpion bolts. Since the Night King has Viserion tearing up the skies, you can bet that contraption will be needed in the wars to come. Coupled with some of Jon Snow's dragonglass supplies and Bronn's perfect aim, the Scorpion bolt could be a crucial player in season 8.
Until that day of reckoning arrives, it seems Jaime will have one final order of business to see through. The Lannister and Greyjoy alliance will return with a vengeance, and there’s no doubting Jaime will play a role in the coming war. Whether it comes before the battle against the White Walkers, during it, or well after, he will be focused not merely on staying alive. His sights will be set on his sister and their child. Will he let them live on, or will he be forced to take action and end the reign of the Mad Queen?
In season five, we learned from Maggy the Frog that a younger, “more beautiful” queen would depose Cersei’s reign. That same prophecy (at least in the books) called for the death of her three children and the Valonqar, the "younger brother" to choke the life out of her. While it remains to be seen if this part of the prophecy will play out on the show, Jaime may well be the man to put an end to the madness and sacrifice his sister for the good of the Seven Kingdoms.