The story of Stranger Things started with Will Byers going missing in the Upside Down. The very first episode of season 1 is called "The Vanishing of Will Byers". It's pretty much clear that Will is a central character and he will be very important in defeating Vecna.
Will Byers seems to have a connection with Vecna. In season 4, Will was able to sense the presence of Vecna. Whenever Vecna is near, Will has a strange sensation on his neck. As we await the final season, fans are left wondering how Will is connected to Vecna.
First of all, the younger version of Vecna aka Henry Creel clearly resembles Will Byers. Both were sensitive kids who were misunderstood by people and faced bullying. While Henry Creel was hated by his parents, Will also faced emotional trauma from his father Lonnie Byers.
In Stranger Things, there are a lot of parallel shots that show Will Byers and Henry Creel are pretty much similar.
Henry Creel and Will loved to draw with both of the characters eventually creating the picture of the Mind Flayer. The main difference is that Will was loved by his mother, brother and friends while Henry was all alone and eventually used his powers to kill his family.
Henry might have seen a reflection of himself in Will Byers and wanted him by his side. Earlier he tried to recruit Eleven but that did not work out. Hence he decided to abduct Will and took him to the Upside Down during season 1. It could be the reason that Will managed to survive in the Upside Down. However, we don't know what exactly happened in there and it remains a big mystery that is yet to be resolved. We will likely get our answers in the final season.
Another mystery in Stranger Things is that the Upside Down is stuck on the date that Will Byers vanished: November 6, 1983. There is a theory that the copy of Hawkins in the Upside Down has been created by a terrified Will Byers. It has been long theorized that Will might have similar powers to Henry Creel so he could have used it to create the copy of Hawkins.
Since Will Byers returned from the Upside Down, he still has some connection to the alternate world. Now after watching season 4, it is clear that this connection is likely related to Vecna. That’s why he can sense that he’s still alive at the end of season 4. Some people have the theory that Will's connection is likely a sheer chance. They are connected because Will was the first victim and hence he is forever linked to his captor.
Now in season 5, Will might become the villain as he aligns himself with Vecna. We know that Vecna preys on his victims using trauma and Will happens to be dealing with such traumas. Will is secretly in love with Mike Wheeler who does not share the same feeling. The heartbreak for Will Byers can drive him to the dark side.
Or else, Will can become the true foil to Vecna and will be the only one who can destroy him. The likely outcome of the story could be that even though both Will and Henry Creel were similar, the key distinction lies in one being loved while the other goes neglected.