What I do remember is that the Avengers meet Daredevil (Matt Murdock) in passing, sometimes for brief team-ups, and they try to befriend Daredevil. At some point, someone (Clint, possibly?) leaves a note for him, which he naturally can't read. Through various clues, the Avengers conclude that he's illiterate. Cue confusion, embarrassment, and the eventual reveal that Matt is blind. I seem to recall a very strong "friendship" theme - that the Avengers are very keen to help and befriend Daredevil.
Is it on the AO3? Maybe...I've been looking and while I've found a few "Avengers don't realize Daredevil is blind" stories, I haven't found one where they think he's illiterate. But of course I could be using the wrong search terms to turn up the particular story I'm looking for.
Thanks for any help!