Myon:

> Head out of the shrine, passing through walls as needed, in the direction of the nearby body of water.

Youmu:

> "Wait. Marisa, can you walk by thy box again?"
> If the box glows again, try opening it while it glows.

> You head for the pond you saw.
> It seems fairly well taken care of, there's even a tortoise in it. Or, maybe it's just a big turtle?

> Marisa does so, wondering what you're getting at.
> You twist the key in the moments it glows, and the box opens up, releasing some hot smoke.
> Though, the smoke soon dissipates...
> You can see something inscribed inside the box, though aside from it, nothing else appears to be present.
> It reads: Open in Twilight. The text feels a bit weird to even look at.
> "What the hell was that?!" Reimu jumps up while you're in the middle of reading it.
> "Was that a spell?" Marisa covers her mouth. "It looks like it went bad or something."
> "What was that magic?" Alice questions, seemingly arriving with Miko once more.
> Aya doesn't chime in. You wonder if she's busy with something elsewhere in the Shrine, or if she just left.
>_

> Ugh, misunderstandings...
> In an echoy voice affirm "We do not wish to take your tower..." and dispel the orb.
> Turn towards Sakuya and continue "We assume their little experiment can stay provided they don't cause any problems...  It's made of ice after all and will only be here until they find something more interesting to pursue."

> "Likely, though I hope they don't take this as a green light to do other things near the mansion." Sakuya responds.
>_

That and unrealistic fantasies, like Okuu's nuclear fusion reactor. Basically anything that falls into obscurity, y'know, beyond the "border of common sense". And thing is, line between than and modern/relevant stuff is pretty fragile. An old mobile phone and (in retconned CoLA chapter) a handheld console are mentioned as objects that fell into Gensokyo. I feel that's what Yukari means in that "cruel, cruel thing" quote.

Dreams/Fantasy vs Reality/Science

Note that this is does NOT mean magic vs technology, as evidenced by kappa, tengu, Kanako and even lunarians.

I was meaning to ask this a while back, so here goes! I think Touhou's themes are too broad and complex to capture in a single character, but anyways here goes. Touhou broadly covers several central themes:

Dreams/Fantasy vs Reality/Science
If I had to pick the singular central theme in Touhou, this would be it. The world of Touhou is literally called the land of fantasy, after all, and the border that separates it from our world is both a physical one and a ideological barrier. In Gensokyo, fantastical is the norm, while in our world, we live in a scientific age where belief in fantastical things such as youkai is at an all-time low.

The sort of dreamy "is this fantasy or reality" trope is touched upon many times in the series, most notably in the lyrics of Innocent Treasures, which directly references the story of Zhuangzi and the Butterfly. The music CD's in general lean much more heavily into this theme, as they follow around the future Hifuu Club, which lives in a dystopian future where children don't smile and natural bamboo no longer grows. There, the harsh, advanced, and scientific reality is contrasted sharply with the fantastical, dreamy, yet unforgiving land of fantasy, Gensokyo. I would really recommend reading all the CD stories as it's some of my favorite worldbuilding and writing from ZUN.

Nostalgia, Culture, and Faith
Relatedly, Touhou as a whole is heavily driven by nostalgia and respect for "outdated" culture. ZUN famously declared EoSD "A 20th century shmup for the 21st century", and was his way of channeling his love for shmups, which even at the time were already starting to decline in popularity.
He loves respecting tradition and doesn't always believe that the modern or scientific way of doing things is the best way.

Gods, traditions, and legends, all cast away by our scientific age, find a new home in Gensokyo, as long as they have believers and thus faith.
The whole "faith" idea (that gods and beings in Gensokyo derive their life force from people's faith in them) is a pretty interesting concept introduced in MoF. It's sort of a meta-thing too, in that ZUN brings awareness to old and forgotten gods, legends, and stories through his works, thus increasing their faith and giving them a sort of "second life" in our world.

Acceptance and Social Order
As mentioned by Cyber, another theme in Gensokyo is that it is all-accepting. Major troublemakers settle down and just join in on regular life after their incident/game is over. What's interesting about this though is that Gensokyo is actually bound by a pretty strict social order where everyone has a role to play -- youkai and humans have a special relationship where humans actually supply youkai with the faith necessary to keep them alive, and humans native to Gensokyo are actually off-limits to the youkai. The protagonists (mostly Reimu) are the ones responsible for resolving youkai disturbances, and all battles are bound by the honor system of rules that is the Spell Card Contract.

Kind of rambly and not what you were looking for but that's my thoughts.