The following contains major spoilers for The Vampire Slayer #3, available now from BOOM! Studios.
For as long as Buffy Summers has been the Slayer, she has had some of the most endearing allies she could have possibly asked for. Apart from the Watchers sworn to assist her or the undead romances found along the way, Buffy's friends in the Scooby Gang have made it their mission to help Buffy in any way they can. In the world of The Vampire Slayer, that has come in the form of taking away everything that made Buffy the Slayer in the first place. Unfortunately, that power found a new home in none other than Willow Rosenberg, and it's driving her towards an early turn into the darkness.
The Vampire Slayer #3 (by Sarah Gailey, Michael Shelfer, Valentina Pinto and Ed Dukeshire) finds Willow, Giles, and Xander all pondering what to do about their current crisis. After taking on Buffy's trauma and subsequently her role as the Slayer, Willow discovered she had also stolen Buffy's memories. As such, Buffy has become a meek, almost aimless version of her former self, while Willow has only gotten more aggressive towards everyone around her. Snapping at Xander for making constant jokes is one thing, but Giles' observation that Willow's magic is "off" somehow comes as a genuine cause for concern, especially considering her original trajectory.
Willow has been an indelible part of the Buffy-Verse since the very first episode of the 1997 television series. "Welcome to the Hellmouth" introduced audiences to Alyson Hannigan's then meek, mild-mannered Willow. Over the years, she would drift away from those diminutive roots and become the Scooby Gang's most outspoken member, as well as its most powerful by a wide margin. This began with the Season 2 finale "Becoming, Part Two," in which Willow used magic to restore Angel's soul. While this was more miraculous than anything at the time, was also indicative of just how much power Willow truly commanded.
Over the years Willow's power would only grow greater, leading her to defeat the Hell goddess Glory, bringing Buffy back from the dead, and even activating multiple Slayers at once. At a certain point, however, it also brought Willow to the verge of single-handedly ringing in the apocalypse. Following the death of Willow's girlfriend Tara, she was driven to find a way to undo things. When that proved impossible, she instead decided to wreak death and destruction upon those responsible, and eventually the rest of the world. Luckily, there was still enough of Willow's humanity left that Xander was able to talk her down from ending it all, but that version of Willow hadn't stolen powers that were never hers, to begin with.
Taking the character's entire history into consideration, if Willow really is beginning to suffer from her own spell, that could lead her down a dark path, and she might just be what destroys the Scoobies entirely. Since none of the others have any powers of their own to fight back with, they would be incapable of overcoming an out-of-control Willow should she set her sights on them. Then again, Willow's magic isn't nearly as strong as it was the first time around, and she doesn't have any real idea of how to put her abilities as the Slayer to proper use, either.
With characters such as Faith and Spike showing up to complicate matters in the world of The Vampire Slayer, there is always the possibility that their presence could be enough to tip the scales out of Willow's favor. It isn't certain that she will become another evil version of herself, but it almost guarantees that Willow will not be able to keep the powers she has attained, at least not permanently. Hopefully, returning the mantle of Slayer to its rightful owner won't come at the expense of anyone's soul or life.