Ah, eyy it's you from the ratatouille meme comment haha. Just wanna tell you the letters are from the blind Noona, not the Uncle. Jingi asked her to send them saying "Please send the thing on the 5th" at the end of chapter 20.
And what Myeong-il saw, in my theory, is a photo. A very disturbing photo, that made Myeong-il vomit from just one look. Jingi asked the Noona to develop the photos (flashback in chapter 34) then send it to him.
I think the letter contains photographic evidence against the creepy Uncle. But Myeong-il just saw the incriminating photo and misunderstood Jingi.
Haha lol yeah it's me again but thanks lol I got too focused on the uncle I kinda forgot and so spot on I just reread that one part where it's her "pov" and jingi gives her rolls of tape for her camera so yeah I think you're right
Oh my God I'm too sleepy for this now you literally just mentioned that....goodnight and thanks lol
All the details that suddenly emerge with this huge clue...suddenly I want to reread
Anyways...if I had to guess about the letter...sexual harassment from his uncle? I'm thinking dried up cum as a "gift" and a shitty message with it. But would that be strong enough to evoke vomit? The way the letter is folded excludes pretty much everything else though...unless its a ...pic printed small enough. Ugh to torment the victim for so long...evil...not to mention the power the uncle holds over him and his brother. No wonder he gets so mad at heonjae when he messes up....hes prpbably trying his best for both of them...but then again...why wouldn't he get the letters if they're from the uncle? He'd want it delievered instead of blocking his access. Unless it's someone else doing that? Not that he'd be the only sender...idk anymore....just wow..