For some reason literally every max Mayfield fanfic I've read it's Steve's sister and it kinda gave me and idea. I really wanna see how it turns out no pressure for you to write it but you can I would love to read it.
Ok so, obv in the first season Steve and his sister's relation wasn't good. Imagine if in season 2 instead of forgiving him like in every other season, she doesn't forgive him. In season four she may not hate him but she still doesn't let her guard down around him bcs of how he treated her. In season 4 when max was cursed by Vecna, she somehow figured out a way by which she can have Vecna take her instead and not max but she doesn't tell It to anyone. Knowing that the only way she can save her lover is by sacrificing herself, she begins to let her guard down with Steve (yk like hugging him or speaking in a softer tone with him). Steve thinks that he can finally build a good relation with his sister after this is all over only to come out of the upside down and find out that his sister is in a coma with several broken bones.