Steve’s mind gets fucked up really bad by some Upside Down baddie, maybe Vecna wreaked havoc in there to send a message, or maybe Steve died and was hastily and desperately brought back, but either way it left him alive but almost completely nonfunctional. He can’t really do anything besides stare blankly, with only the vaguest hints that he’s aware of his surroundings. He’s basically a walking coma patient, and it breaks everyone’s hearts but they resolve to take care of him and try to bring him back. I didn’t have a fully formed idea about this, just little sparks of inspiration like Dustin cuddling him and letting out little sniffles as he pulls Steve’s limp arms around him to simulate a hug, or Robin rambling to him and getting more and more upset the longer he just lets her talk, or Eleven trying with increasing desperation to reach his mind only to be blocked at every turn. Would prefer a happy ending, but wouldn’t say no if someone wants to turn it dark and have Steve helpless against someone with dark intentions ;)