I've always felt bad for Renko, because no matter what Maribel's relation is to Yukari, in the end Renko is still the one that gets left behind. She's the side character that nobody really cares about.
Kinda wish I was a moonspeaker so I would know how that doujin relates to that complicated theory of yours.
Speaking of complicated theories though, I have one where Renko becomes
Yuyuko.
Yuyuko is common, and honestly thinking about it kinda not fit with things.
And I know Byakuren sounds even more ridiculous, but consider these: 1. The only two Touhous with lotus "連,ren" in their name. Renko pretty much means "Lotus Girl/Child" or "Young Lotus" 2. During her "power up" in Merry's dream in Trojan Green Asteroid, what was her power? Flight and super speed/strenght. What theme song was playing? Emotional Skyscraper ~ Cosmic Mind 3. Being in Gensokyou can be said to be their dream. Renko wanted to go there, and Byakuren wished for a world where human and youkai are equals. 4. With how Renko and Maribel story goes, it won't be strange if Renko eventually end up be a casualty and thrown into the gap or the sort. Merry would try to search but cannot locate her. 5. There's no interaction between her and Yukari in canon, but that doesn't exactly mean they haven't or have either. In other words, there's nothing to support or contradict it.
Still, this is just wishful thinking, which I only considered after reading that book. Nothing set in stone or anything.
I didn't realize Renko being Yuyuko was that common, though I can't say I'm surprised by it. If you happen to know of any doujins (preferably with translations) that feature that, please share them.
As for how I came to that theory, I never said it made sense. In fact, I've been trying to figure out how to rationalize the differences in their powers, and so far I've been unsuccessful. My main basis for it is that both Renko and Maribel, and Yukari and Yuyuko are very close friends. So yeah, pretty flimsy as well.
I should probably reread the stories for the music CDs, because I completely forgot that that happened in Trojan Green Asteroid.
... that Isn’t canon, right?... I hope it’s not canon! It’s cannot be canon! It hasn’t been canon! Right? Right?!
That Maribel Hearn and Yakumo Yukari are the same person in some fashion? More or less accepted, last time I checked. Their last names are a giveaway .