
I have a theory that Yui is a dude. Like maybe it's just me, but let me explain!
Notice how Yui has short hair, that like a male? Maybe this is just the authors lack of skill in drawing long hair, but NO, OTHER GIRLS HAVE LONG HAIR! Then I thought it's probably just a coincidence, but maybe not. My next reason is that she has no tits.
http://www.mangago.zone/read-manga/akai_ito_no_shikkou_yuuyo/nmt/c001/16/
http://www.mangago.zone/read-manga/akai_ito_no_shikkou_yuuyo/nmt/c001/9/
And look at her neck, it's very similar to other males in that manga.
Now look at both Kei and Yui's close up shots.
http://www.mangago.zone/read-manga/akai_ito_no_shikkou_yuuyo/nmt/c001/17/
http://www.mangago.zone/read-manga/akai_ito_no_shikkou_yuuyo/nmt/c001/30/
Their face stucture is also very alike, and Yui's sort of drifts from the usual female.
This could just all be me grasping at straws and some people probably think I'm a just a crazing fuck, but hey, what can you do? ╮( ̄▽ ̄)╭ I just wanted to know it anyone agrees.

You Jin, you are so fucking cute
http://www.mangago.zone/read-manga/youjin/uu/youjin-chapter-16.2/9/

Got any raws?

http://www.yaoiotaku.com/forums/threads/42789-akai-ito-no-shikkou-yuuyo-yoshio-akira-%5Bjp%5D.
I already had a post a comment down how to search for raws.
I died when SA talked about elementary school kids drawing dicks of everything... In my time, we never did that shit ╮( ̄▽ ̄)╭
Yeah I remember boys drew them but girls didn't. Already a fujoshi at such a tender age lol!
OH GOD LOL no I swear I wasn't the only one/girl who did this!! *sweats nervously* I want to say it was a 90's kids thing.. but.. it probably wasn't and I just had a really elementary school experience.. :')