Caution: spoilers ahead for The Expanse book series
Cara's brother is miraculously revived in The Expanse season 6; how does this Laconia mystery set up a future villain from the original books? Each and every installment of The Expanse season 6 begins with an update from Laconia, centering around young Cara, the daughter of scientific researchers. Laconia is one of many systems that became accessible via The Expanse's Ring Gate, and was chosen as the perfect destination for Sauveterre's Martian defectors - largely thanks to the abandoned Protomolecule warship left carelessly parked in the sky.
But while Laconia's military presence is looking upwards, Cara is finding some curious Protomolecule activity down on the ground. Deep in the forest, she encountered a breed of strange dogs that "fix" things - even life forms - using their unique connection to the Protomolecule. So when Cara's brother, Xan, is killed in a tragic accident, she knows exactly who to visit, dragging Xan's corpse to meet her new canine friends. Sure enough, the dogs resurrect Cara's brother in The Expanse season 6's fifth episode, ("Why We Fight"). But more than simply expanding Protomolecule mythology and highlighting the importance of road safety, Xan's not-quite-right return paves the way for The Expanse's new major book villain - Winston Duarte.
The Expanse season 6 has already debuted Dylan Taylor as ex-Martian admiral, Winston Duarte. Leading the Laconian defectors, Duarte first appeared onscreen at Xan's wake, and in James S.A. Corey's original books, at least, he inherits The Expanse's main antagonist mantle from Marco Inaros. Introducing Duarte with only 2 episodes remaining in this (supposedly) final season was already unusual, but Xan's Laconian revival foreshadows Duarte's evil intent further. Paolo Cortázar's cameo in The Expanse season 6's fourth episode clearly positioned Duarte as the driving force behind reawakening Laconia's dormant Protomolecule battleship. That means Duarte not only hopes to wield the Protomolecule as a weapon of war - but he's also that rarest of villains who actually appreciates the Protomolecule's interconnected, near-sentient nature.
Xan can now count himself part of that interconnected blue network. When Cara reunites with her undead sibling, Xan's eyes are obscured by an eerie dark glaze, while his personality and speech don't seem entirely human either. Compared to the eager, excited boy from before, there's now a vague detachment in Xan's voice, exemplified when he stares into nothing and creeps out every single viewer by remarking, "I never saw that before..." The Expanse is signalling Xan as a new addition to the Protomolecule's network - the very same network Winston Duarte is hoping to crack. And in the Expanse book series, Duarte seeks immortality through the Protomolecule - similar to the process Xan just experienced, but refined and perfected by Laconia's scientists. The first major step toward achieving this aim comes when Duarte's soldiers capture Xan, and bring the little creepster to Cortázar for poking and prodding.
By including Xan's weird revival in season 6, The Expanse is continuing to ready Winston Duarte as a major force in the show's future. Which is strange, considering The Expanse season 6 is billed as the Rocinante's last flight by Amazon. Episode 4 introduced Duarte as a live-action character, now episode 5's Xan storyline is setting the board for his endgame. Almost certainly, The Expanse has something in mind for continuing the story and adapting James S.A. Corey's final 3 books somehow, in some way, in some form. Because season 6 isn't just leaving the door ajar for more The Expanse - it's sending Amos Burton to kick off the hinges.