Magus said: It's canon that Aya can make her wings disappear, so why not Flandre?
It's not canon. Though there has been discrepancies regarding whether she has wings (including within a single book), it was never actually stated that her wings can disappear, just speculation.
Anyway, it's obvious that the artist is making Flandre look like Rumia deliberately, what with that signature ribbon belonging to Rumia.
There are canonical depictions of Aya both with and without wings. Obviously that means she can make them disappear, unless you want to say they were amputated between appearances. And if Aya can do it there's no reason other winged Touhou characters couldn't too.
Magus said: There are canonical depictions of Aya both with and without wings. Obviously that means she can make them disappear, unless you want to say they were amputated between appearances. And if Aya can do it there's no reason other winged Touhou characters couldn't too.
Or the chance of errors. It would make for a good doujin ideas, yes, but Aya has been depicted with wings in only Perfect Memento in Strict Sense and Bohemian Archive in Japanese Red, the latter being quite notorious for being extremely inconsistent in the characters' features. Also, Aya is depicted without wings in all official games and manga. Hence, parsimony leads to at least two conclusions: that Aya's wings are retractable and that there are errors in her depiction. With both being equally possible, it is only logical that no assumption is taken to jump to conclusions.
A similar example would be Tewi's position in Eientei. In Silent Sinner in Blue, she is shown to be on at least equal levels with both Eirin and Kaguya while she refers to them as her masters in Inaba of the Moon and Inaba of the Earth and Strange and Bright Nature Deity. Unless you wish to take an extra assumption that her rank in Eientei changed from the landlord to a subordinate between appearances (which goes against the law of parsimony) I should say that this is an error and an inconsistency, there is no reason other depictions including Aya's wings could not be.
Mind you, I in fact am in support of the retractable wing theory. Just that it's not officially confirmed.