I have a weeaboo horror story. Unfortunately, the weeb in question was me.
I was a delusion-flavored mess when I was in eighth grade. I didn't fantasize about Kawaii Desu Japan (I had brothers in the military who shared their photos of "No whites allowed" signs on Okinawa) and I didn't own a ton of anime or merch or anything (no allowance, no job), but my best friend and I were both weeby weird kids with mental problems and somewhere in late junior high we went full-on otakukin.
I won't go into too many specifics, but we fixated on a couple of characters from the Final Fantasy series and constructed this elaborate scenario explaining how we came to be in our current bodies. Anything could be proof: waking up sore meant your real self had been in a fight, an abandoned scarf in the park was actually a gift from your original world, etc. We were two creative, skewed individuals with no social lives, and we pretty much had ourselves convinced that we were going to break out of our current forms and return to our real power eventually. (I even drew a short comic about us using our powers to kill all the people who picked on us at school.) We traded stories about signs we had seen, significant dreams we had had--anything reinforced this idea that we were special, destined beings.
Thankfully I wasn't really into the Internet at the time; my activity online was limited to roleplaying on a single sci-fi board and reading stuff on fanfiction.net. If either of us had run into an otherkin/otakukin group, we might've fallen even further down the rabbit hole. As it happened, we went to different high schools and thus broke up the folie a deux, while I had a mental breakdown in my freshman year and wound up getting moved to special ed. Medication and therapy did the rest.
My friend and I reconnected late in our high school years, but we were plain old humans again. She's into Adventure Time and MLP now, while I skew more towards murder mysteries and romance novels. We're still in contact, and still call each other by our 'real' names, but it's not a serious thing any more. Thank God for that.
Sorry for the TL;DR personal stuff, guys
. Some of the stuff on that Weeaboo Stories blog sound pretty far-out, but I know from firsthand experience that if you're lonely and crazy enough, you can convince yourself to pull the nuttiest otaku-est crap imaginable.