For me it was by watching Junjou Romantica in Youtube when I was 16. I mistook Misaki with a girl and I thought it was shoujo. So, it was a real shock for me, I didn't even know yaoi existed in general and I was super innocent even at that age. Anyways, at first I felt disgusted (I grew up in a quite homophibic family), but after that shock I became curious and kept watching. Now I only read yaoi lol.
For me it was by looking completed animes on YouTube and I found Junjou Romantica, I was 13 or 14 at the time and I was starting to like anime so it was kinda shock but I became curious and here we are ╮(￣▽￣)╭ reply
