Let's make up some stupid theories!

[Esoterica]

Reimu. :V

Brown hair
Friends with Yukari
Five letter name beginning with the letter R

It all fits.

[Marin The Magus]

Brown hair
Friends with Yukari
Five letter name beginning with the letter R

It all fits.

Both names begin with "Re" (YES I'M USELESS!!)

[Myschi]

Looking at KrackoCloud's avatar blew my mind...

Satori's eye is

Spoiler:

actually Kracko, minus the spiky cloud.

[Drake]

Looking in the mirror blew my mind...

My eye is

Spoiler:

actually Kracko, minus the spiky cloud.

[Esoterica]

ITT Drake is a cyclopes.

[Ryuu]

Flying isn't a special ability.

Really, everyone can fly, but no one is taught how until after a certain age for safety reasons. This is why Reimu was first seen flying on top of Genji; she simply wasn't old enough to fly yet.

[Fightest]

Flying isn't a special ability.

Really, everyone can fly, but no one is taught how until after a certain age for safety reasons. This is why Reimu was first seen flying on top of Genji; she simply wasn't old enough to fly yet.

It goes further than that. It's not flying that's the special ability. It's staying on the ground. Without the utmost concentration and self-discipline, everyone in Gensokyo would fly off into the sky. Rumour goes that the invasion of the Moon might have been an accident...

[Marin The Magus]

People, you are all crazy.
The only reason why everyone in Gensokyo can fly is because of the same reason they almost never age (You can't say that Reimu and Marisa aged ??): They ALL are Peter Pan And The fairies are the ones that make them fly, that's why Reimu had Genji, because in HRtP she didn't meet any fairy.

[Tengukami]

Eirin is the real power behind holding the Hakurei Border together, since Reimu relinquished it to her. This was done because Reimu was too easy a target, and even with the spellcard rules, she was in danger. And if Reimu went down, so would the border. Therefore, she put Eirin in charge, secretly, so that Reimu would continue to be a false flag decoy for any anti-Gensokyan operations.

[Lord Phantasm Satori]

rinnosuke is rikako after a gender change.

[Feather Black]

I don't know if it was posted before but considering the doujin Touhou Kourinden, Tokiko is the daughter of Keine and Rinnosuke.

Since Youmu is a gardener, her mighty weapon may not be her two swords, but a lawn mower provided by Yukari from real word. (not the best stupid theory I have)

Reimu and Marisa never age because they may have finally eaten Mokou's guts, after all... So, Marisa's wish about being immortal is to fool us, people !

If all Touhou people can fly, it's because Suika loves messing with gravity laws. A lot.

Nobody in Gensokyo are human. They're items, in fact.

That's all.

[Myschi]

I don't know if it was posted before but considering the doujin Touhou Kourinden, Tokiko is the daughter of Keine and Rinnosuke.

Reimu and Marisa never age because they may have finally eaten Mokou's guts, after all... So, Marisa's wish about being immortal is to fool us, people !

That first one makes all of my Tokiko/Rinnosuke images awkward now.

Also. Mmm... immortal organs~ The best kind'a organs.

[Stuffman]

Yukari is actually not strong at all. She can move stuff around with gaps but she's pretty terrible with danmaku. Whenever we see Yukari fight, it's actually Ran pretending to be her! Ran is the truly strong one; Yukari uses her to maintain the facade that she's one of the most powerful people in Gensokyo. Why do you think she picked a kitsune, a master of illusion, as her shikigami?

Naturally, Chen has to pretend to be Ran sometimes to fill the gap, and if all three of them are in play, Chen has her own secret shikigami.

[Nobu]

Yukari is actually not strong at all. She can move stuff around with gaps but she's pretty terrible with danmaku. Whenever we see Yukari fight, it's actually Ran pretending to be her! Ran is the truly strong one; Yukari uses her to maintain the facade that she's one of the most powerful people in Gensokyo. Why do you think she picked a kitsune, a master of illusion, as her shikigami?

Naturally, Chen has to pretend to be Ran sometimes to fill the gap, and if all three of them are in play, Chen has her own secret shikigami.

This theory tickles when you think of Necro Fantasy vs Necrofantasia :3c

[Fightest]

Yukari is actually not strong at all. She can move stuff around with gaps but she's pretty terrible with danmaku. Whenever we see Yukari fight, it's actually Ran pretending to be her! Ran is the truly strong one; Yukari uses her to maintain the facade that she's one of the most powerful people in Gensokyo. Why do you think she picked a kitsune, a master of illusion, as her shikigami?

Naturally, Chen has to pretend to be Ran sometimes to fill the gap, and if all three of them are in play, Chen has her own secret shikigami.

She may not be good with danmaku, but she can be very precise with her gaps. Where do you think all the stray shots from all the other danmaku fights go?

[Lord Phantasm Satori]

ran is actually an abandoned mech prototype from beyond the border. Her mugen character proves it!

[Savory]

Kanako didn't really want to start an industrial revolution when she convinced Utsuho to get Nuclear Power. Kanako really wanted faith; she knew Okuu would go mad with power and cause an incident by going on a rampage. Then, in the midst of things, she could come forth and saved the day. What she didn't count on was the heroines and Okuu's warped sensibility  from attaining her new power.

[orinrin]

Remilia is a ⑨けつき.


*SupremeBogus is shot*

[Marin The Magus]

Sanae is actually Sanae Hanekoma, from "The world ends with you".
 

[Romantique Tp]

I think the unnamed miko in this ZUN art looks a lot like Rin Satsuki.

[Myschi]

I think the unnamed miko in this ZUN art looks a lot like Rin Satsuki.

So that's where she's been...

[Blackraptor]

All of Windows Gensokyo is actually a Reality Marble created and maintained by Mima who is sealed inside the Hakurei Shrine. It is uncertain what would happen if Mima is released which is why no one was told that she was there just to be safe.

[Phlegeth]

Cirno comes from one of the strongest families in the outside world.  Her father was a human and her mother was a fairy.  At first it was good, all of her step brothers and sisters (100% human) loved her treated her like family.  But after their father died, they became annoyed with their eternal youthfulness and chased them back to Gensokyo.  However her mother stayed and turned and gave her this message, "Never forget your pride, you are a member of the strongest family."  Over the years she forgot most of it and it became, "Never forget you are the strongest!"

Also proof is in the eyebrows.  She has Mugi eyebrows.

[Tengukami]

That's ... actually pretty heartwarming.

[Marin The Magus]

Cirno comes from one of the strongest families in the outside world.  Her father was a human and her mother was a fairy.  At first it was good, all of her step brothers and sisters (100% human) loved her treated her like family.  But after their father died, they became annoyed with their eternal youthfulness and chased them back to Gensokyo.  However her mother stayed and turned and gave her this message, "Never forget your pride, you are a member of the strongest family."  Over the years she forgot most of it and it became, "Never forget you are the strongest!"

Also proof is in the eyebrows.  She has Mugi eyebrows.

It's surname, plz? xD
And btw, how was a fairy unnoticeable in the human world ?

[Blackraptor]

And btw, how was a fairy unnoticeable in the human world ?

Her family lived in Akiba.

[Phlegeth]

Also it was point in history where people stopped noticing fairies and other weird stuff just because they didn't want to.  And Kotobuki, it was a K-On joke  :V

I had to go to wikipedia to find out her last name too.

[?q]

So, Muse.  Not the band, but the Mary Sue par excellence who takes up 2/3 of Kioh Gyoku's playtime.  It is my belief that her overpoweredness stems from her secret purpose as ZUN's offshore design dump.  Consider:

*She has perfect and elegant complete mastery of throwing knives.
*Her blue-white maid outfit is fairly popular...
*...as is a prominent black ribbon with a red brooch, certainly a unique color schema.
*She's a vampire...
*...and an alchemical magician...
*...actually make that a magician that carries a doll and uses exploding puppets as weapons.
*I'm sorry, did I say exploding sub-enemies?
*She also has a long black cape...
*...and hails from the "future earth".
*She can manifest her wings on command...
*...and can abuse her alchemical skill to warp HERSELF into any form she wants.
*Nobody knows her age, except that she's been around a long time.
*She's a controversial figure in her time insofar as whether her motives are pure...
*...speaks little unless provoked...
*...and is part of a family that wishes to merge science with fantasy.

As a side note, not only is it entirely possible for Sakuya to be based on Muse according to the time of Kioh Gyoku and EoSD's releases, but the strikingly similar color schemes between the two actually FAVOR this postulation; overthrowing the previously-held belief that Sakuya was based on a certain PC-98 maid.  This could shed some light on ZUN's motivation for sweeping the PC-98 era underneath the rug - specifically, he hates that cheap spawn-of-Satan Stage 5 boss like everyone else.  To contrast, the black-red cross she carries and the cape she sports when she gets serious is likely a throwback to ZUN's (and every other non-Mima fan's) favorite PC-98 character.

As of the release of Undefined Fantastic Object, the only aspects of Muse that have not come to light are her knives' target emblems (which look suspiciously like the spell circles in the fighting games) and that one spell card that features pulsating full-screen tunnel action (co-opted by Shinki in Phantasm Romance before ZUN could get around to it). 

Thus, following TH12 ZUN was clearly out of ideas.

[OkashiiKisei]

Muse as base for several Touhous.

Though we have yet to see anyone use a ginormous evil scepter like her (Mima is pre-Muse, and her scepter doesn't look anything like it, so yeah).

At least, it looked more like a spear/scepter to me rather than a cross...

Point is: a future Touhou will wield a huge spear/scepter/staff o' darkness.

[Blackraptor]

The Reimu and Marisa in the PC-98 games are not actually the Reimu and Marisa of the Windows games. The PC-98 Reimu and Marisa are actually ancestors of the Windows heroines, they just happen to have the same names. This accounts for the differences between the two sets of heroines, the utter disappearance of several PC-98 characters from Windows games, and even why Alice suddenly showed up PCB as much older than Lolice in MS.

Going by this, the PC-98 games happened in the distant past when the Hakurei line was also on the verge of extinction for one reason or another. That Reimu's exploits increased the faith and dependence of people on the Hakurei shrine and the clan eventually recovered...until the Windows games happened.