WARNING: The following contains spoilers for X-Factor #5 by Leah Williams, David Baldeon, Israel Silva & VC's Joe Caramagna, on sale now
The X-Men may have been victorious in X of Swords, but the heroes still have plenty of enemies and threats to deal with outside of other dimensions like Otherworld and Arakko. In fact, one seems to have made it's way to Krakoa itself, leaving a classic X-Force leader unexpectedly dead.
In X-Factor #5, Siryn just fell to her death, despite her ability to fly, which opens up the question of what actually killed her. There's a chance that it could be connected to her minor role in X of Swords, which in turn could endanger every single mutant on Krakoa.
Following the chaos of X of Swords, Krakoa is initially a place of happiness and joy once again. The Five have begun restoring mutants again and are working heavily with X-Factor to investigate any other mysterious deaths that come to Krakoa. They're able to restore Wind-Dancer, one of the Academy X-era New Mutants of the '00s, which allows her to reunite with her old friends after being freed from her commitment to Mojoworld following her demise at the hands of a reluctant Adam-X. Even with the Rockslide they knew seemingly gone forever due to his demise on Otherworld, Eye-Boy has committed himself to help the newly formed version of Santo adjust to living on Krakoa with the rest of the mutants as they celebrate their reunion.
However, all these celebrations are punctuated by a surprising and sudden scream that overtakes the night sky. Tracking it to its source, Northstar and Aurora are shocked to find Siryn, a long-time X-Man and hero, dead in a heap on the ground. This causes some serious concern for the heroes, despite their ability to resurrect mutants thanks to the Five. One of the first concerns is how did Siryn -- who has long had the ability to fly -- find herself grounded in such an inglorious manner. The immediate possibility is that somehow, her powers were removed mid-flight, which could have caused Siryn to fall to her doom.
While that idea is worrying enough, another far more worrisome prospect could be the cause, too.
During the events of X of Swords, the First Horsemen unleashed a sneak attack against Apocalypse and his allies from Krakoa. Part of this assault included a poisonous arrow fired by Pestilence, which spreads a terrible infection into its target. The virus unleashed was enough to kill anyone who touched an infected victim in Otherworld, with even the massively powerful Saturnyne warned against getting too close to her toxic spread or risk losing her life. In the chaos of the sneak attack, Rictor was struck by one such arrow, and he even eventually succumbed to the infection when back at Krakoa. However, it's worth noting that Siryn rescued him, grabbing her former X-Force ally by the arm and dragging him back to Krakoa.
Although Siryn hadn't initially shown any signs of infection, it's possible that Pestilence's impact on Krakoa hasn't been fully felt. If the Pestilence disease did transfer to Siryn, it would explain what could have killed her mid-flight. It would make the arrows of Pestilence a far more deadly tool than anyone expected, and it could even give one of the First Horsemen a bigger impact on the fallout of X of Swords than any of her kin. If this was the cause of Siryn's death, then there might be a seriously dangerous pathogen traveling through Krakoa. It could infect other heroes on the island and potentially even spread to the Five, which could disrupt the X-Men's ability to restore their fallen comrades and take away one of the greatest advantages the X-Men have developed since forming the island nation.
Even if X of Swords is over, the prospect means that mutants could be dealing with the fallout from the event for a long time to come.