I pretty much adore all of the Mountain Pukuichi works, and this one is no exception. It also makes me feel more and more as if there should be a general Drama
tag associated with all of them...
Maybe not all of them, I would say this one and Two of Us. And in her Author's note in Two of Us* she pointed out that normally she just does "heart-warming" yuri manga, but occasionally she likes to write more dramatic stories (like this and "Just the Two of Us")
Nana yuri is mostly fluff. Yes, the postscript is all "I just thought about death." But if you know Non-non biyori, that's a fluffy, "healing show" with fluffloads of fluffy fluff and subtext yuri for two of the main characters. But one show the tomboy sister teases the easily frightened superstitious sister to the point where she's hysterical and can't sleep. Then she "reassures her:" there's not such thing as ghosts, I promise! When you die, you just disappear forever. Then she spends the rest of the night awake thinking about what she just told her sister. :) Nana yuri didn't even milk the usual "But we're both girls!" thing at all. She just looked it up on the internet and tried out the advice she saw, her best friend won her heart, happily ever after.
As for this story: there are many unhealthy things, but they've admitted that Azusa is heartbroken, that Ui realizes she's a good substitute for her sister to Azusa, that Ui had strong incestuous feelings for Yui, etc. And Ui established that she's willing to dive in to having sex with Azusa on the rebound. Put that way, there isn't much left undiscovered to cause them issues. By the way, I agree with the logic of this doujin: If Yui really was dating someone like Nodoka or Mugi, the way she acts with Azusa would change from cute and clueless to unethical.
*PS Mountain Pikuichi writes long author's notes and so far the two original doujins, the notes aren't translated. I am translating the note for Just the Two of Us now and I will post it in the comments there. The relevant part here is as follows:
"いままではほのぼのゆりまんがばかり描いてきたので
Because up until now I’ve only drawn “heart-warming” yuri manga,
たまにはちょっと階い話かいてみたかったんですすいません。
I just wanted to try writing on another level once in a while - sorry*!"
-- Mountain Pikuichi, Just the Two of Us
last edited at Mar 19, 2016 6:59PM