WARNING: The following contains spoilers for Naruto: Shikamaru's Story -- Mourning Clouds by Takashi Yano and Masashi Kishimoto, available in English from Viz Media.
In the Naruto: Shikamaru's Story -- Mourning Clouds novel, we're treated to an in-depth look at how demanding it is being the Hokage's trusted advisor when the threat of war looms. For years, Shikamaru has been fighting at Naruto's side, but now in the Boruto series, as the two are adults and diplomats, they must figure out how to stop the Fifth Great Ninja War from happening.
The Land of Earth wants to invade the Land of Flowers, which finds Shikamaru exhausting every means -- even using sinister plans behind his leader's back -- to attain peace. Interestingly enough, just when he gets super-stressed out over whether he can deliver for Naruto, Shikamaru encounters Sasuke, of all people, and gets a long-overdue reconciliation with the Ranger.
In the novel, Shikamaru's fed up with trying to get all the nations on board after the failure of the Kage Summit. Instead, he's arranged a Continental Summit for all the feudal lords to vote, hoping the recourse isn't war as Konoha's friends in the Land of Lightning are ready to stand with the Flowers. As he takes a cigarette break in between proceedings, Sasuke passes by, looking to update Naruto on his Ranger missions.
He can tell Shikamaru's stressed so he stops to chat about what's been going on -- having watched it all from the outside. Shikamaru opens up to Sasuke that he's feeling pessimistic, which is why he's called back spies from Iwagakure, as well as Sasuke himself, as their rivals won't like the idea of these powerful shinobi out there. Plus, if war breaks out, Shikamaru will need Sasuke defending Naruto on the frontlines.
Seeing Shikamaru sacrificing so much warms Sasuke's heart and while he's usually frigid -- as seen here when he calls Naruto a "loser" in banter -- he has nothing but the utmost respect for Shikamaru. It shocks the hero as he and Sasuke have never been close at all. In fact, he was jealous of Sasuke's skills, as well as his ability to get girls. In terms of Sasuke's redemption, Shikamaru simply looked after Naruto -- it wasn't about saving Sasuke during their rivalry. However, Shikamaru has always revered him as a powerhouse and has been grateful he chose to work for them again than be a rogue.
And make no mistake, Sasuke's just as grateful to working be under a genius like him. He even labels Shikamaru as the architect of all this, knowing he wants peace just as much as Naruto. As they compliment each other on being sharp thinkers, Sasuke makes it clear that he really is proud of how Shikamaru has evolved and is fighting in the shadows, doing the kind of dirty work Sasuke does on the outskirts.
This dawns on Shikamaru as well, who never thought he'd relate to Sasuke. But as the Uchiha warrior encourages him, Shikamaru truly appreciates the recognition for being a pillar. In fact, they both are, which is why Sasuke says he'll always have Shikamaru's back. He even uses his lightning to light Shikamaru's cigarette, capping their bonding moment and reminding Shikamaru that no matter what, they're all in this together.