Stranger Things' season 5 promises an epic showdown between Eleven and Vecna, but also raises questions about Eleven's extraordinarily gifted sister, Eight, a.k.a. Kali. In Stranger Things season 2 episode "The Lost Sister," Eleven traveled to Chicago to meet Kali, who possessed the ability to manufacture auditory and visual hallucinations in her victims. At the end of the episode, Eleven opted to leave Kali to go help her friends in Hawkins, leaving Kali heartbroken. Kali is only briefly mentioned in season 4 when Henry Creel, a.k.a. Vecna, referred to her departure from Hawkins Lab.
Kali's powers are distinct from Eleven's, and the sisters' skill sets don't overlap. In season 2, this distinction seemed to suggest that each gifted child from the lab had his or her own unique set of powers. However, season 4's flashback sequences revealed that numbers 002 through 010, with the exception of Kali, demonstrated powers identical to Eleven's. Only Henry singularly exhibited both telekinetic and hallucinatory abilities. With the end of season 4 depicting a fracture between Hawkins and the Upside Down, and the Upside Down subsequently seeping into Hawkins, there's a possibility for Kali to return to Hawkins in Stranger Things season 5 to help Eleven defeat Vecna.
Why Kali Wasn’t Killed By Henry Creel At Hawkins Lab
Kali escaped Hawkins Lab sometime before the massacre, as confirmed by Henry. Although Henry knew of Kali's existence, he made no attempt to find her when he returned as Vecna. Because Kali was ostensibly the only child who presented with hallucinatory abilities (as opposed to telekinesis), it is theoretically possible that Brenner chose not to develop Kali as doggedly as he did the other kids whose powers could be utilized remotely.
It seems that Kali's escape from the lab was not regarded as the emergency that Eleven's escape became. While it's difficult to believe that Dr. Brenner allowed Kali to escape, it's plausible that neither Brenner nor Henry considered Kali as powerful an asset as Eleven. While Henry may have planned to hunt down Kali and kill her had Eleven not banished Vecna to the Upside Down, it is equally plausible that Henry simply did not regard Kali as a worthy opponent, making a potential Stranger Things season 5 return an unexpected wildcard in the battle against Vecna.
How Kali's Powers Could Affect The Outcome Of Stranger Things Season 5
Eleven has proven on two separate occasions that her telekinesis is stronger than Vecna's—first, when she opened a gate and trapped Henry in the Upside Down, and later when she escaped Vecna's clutches in the Upside Down. Eleven's most salient weakness against Vecna is that she is not capable of invoking hallucinations in people. However, Kali's abilities closely mimicked Vecna's powers in this capacity. While there is no evidence thus far that Kali can remotely access people's minds to implant hallucinations, Kali could still conceivably affect Vecna's perception if she came face-to-face with him, at least long enough to serve as a distraction for Eleven.
Further supporting Kali's possible return are the love and care Kali obviously holds for Eleven. Kali was devastated when Eleven chose to return to Hawkins. Kali's impetus for leaving Hawins Lab was the abuse they suffered there, suggesting that Kali may have stuck around the lab after her powers were developed enough to escape for the sole purpose of protecting her younger sister. Kali also has a vested interest in defeating Vecna; Kali's goal in season 2 was to hunt down and kill all those complicit in her detention in the lab. While Vecna, in his capacity as a powerless orderly, was likely not directly responsible for the torture Kali endured, he still had a role in perpetuating the lab's interests. Considering Kali's return would serve as both a good way to wrap up a disparate storyline and a compelling weapon in the effort against Vecna, Stranger Things season 5 will need to either explain her absence at the end of the world or bring her back for the final fight.