I hate to say it, but Steve Harrington (Joe Keery) seems the most at risk for me. As a dedicated Stranger Things fan, I've learned that the minute I start rooting for a character, the Duffer Brothers will kill them off. And that's exactly what's happening to Steve in season four.
Volume one kept teasing a possible romantic reunion between Nancy (Natalia Dyer), who is currently dating Jonathan (Charlie Heaton), and Steve. This love triangle drama has gone on long enough in the series, so, it's likely a red herring. It's getting us emotionally invested in the pair before killing one of them, namely Steve, off.
Not to mention, Steve continuously puts himself in harm's way, protecting everyone from best friend Robin (Maya Hawke) to mentee Dustin (Gaten Matarazzo). There's only so many times that this character can evade death. And don't forget, the Duffer Brothers originally wanted to kill off Steve in season one. His clock is certainly running out.