Confused by how many people seem to be familiar with Upper One and Two here

Hello all. I finished watching all of Demon Slayer a couple weeks ago. I have not read the manga. In fact, Demon Slayer is actually one of the only anime’s I’ve ever seen, so I’m still new to it. It was recommended to me by friends.

I figured that, since I finished the show, it should be okay for me to come onto this sub, because posts are flaired based on whether they are about the manga or the anime. So I can avoid spoilers by not reading any manga based posts.

My confusion comes in because I’ve noticed a number of anime based posts (designated by the flair), that talk about Upper Moons One and Two. And they talk about them in detail, but I’m just confused, other than I think a couple of scenes (maybe just one scene) I don’t remember seeing much of them in the anime.

Did I miss something? How do people know so much and talk so extensively about Upper Moons One and Two when I don’t really remember seeing much of them? Unless they are all manga readers commenting on and posting with the anime flair?

Just wanted to make sure I didn’t miss anything.