There is speculation as to why Vecna reveals his identity to Nancy at the end of the first volume. As smart and capable as she is, Nancy isn't usually heralded as the hero of the show, so it seems out of place to have Vecna reveal his past to her. The group is pulled up into the real world when they go to the Upside Down version of Eddie's trailer home. Nancy's journalistic instincts continue to be strong, and she learns about Victor Creel, whose family's deaths hold striking similarities to a Hawkins student's murder.
The episode cuts back to Eleven and Number 1 in her repressed memory, which she is able to access through a specialized isolation tank. Nancy jumps in after Steve after he is dragged to the Upside Down.
Vecna's role in Stranger Things' history cannot be overstated, regardless of how the Duffer Brothers chose to craft the last episode of season 4, volume 1. He monologues about his life as Victor Creel's son, Henry, instead of torturing Nancy about her best friend's fate. Vecna's origin story provides a throughline throughout the fourth season, whether it's an elaborate way to get justice for Barb or a creative narrative technique. Nancy is transported to an empty pool, where she sees a dead Barb, instead of passing through smoothly like Robin and Eddie. To make matters worse, Eleven is in California, so she isn't around to help stop Vecna.
Vecna's unique powers of reaching into his victims' minds and controlling them based on traumatic experiences are far different from the Demogorgon's animalistic tendencies. It's hard to know if Nancy is hearing what Henry is saying to Eleven or if the show's creators thought it would be easier to kill two birds with one stone. It is possible that her feelings for Steve remind her of Barb's death. It is unlikely that Victor is responsible for the new killings because he has been institutionalized for his wife and kids' murders since the 1950s.
It makes perfect sense that Vecna would torture Nancy because Fred and Max are haunted by deaths that they feel responsible for. Before the two episodes of Stranger Things season 4, volume 2 are released, the intercutting between the two scenes serves as a well-crafted cliff-hanger. Why does Nancy need to be aware of this discovery? The first episode of the fourth season of Stranger Things features Eleven unburying her repressed memory. Vecna is able to access his victim's mind by exploiting a moment of trauma. Barb's name is missing from the other seasons despite her death in the first season. Nancy's character seems to be rekindling her romance with Steve.
Nancy is investigating the death of Chrissy in the fourth season of the show. Nancy discovers most of the mystery.