Quite cute, actually.

But in Curiosities of Lotus Asia, it was revealed that the Sumireko in Gensokyo is a doppelganger, and therefore a youkai (while the Sumireko in the outside world is still human)

I guess that's what happens when you go to gensokyo, you'll learn the hard way.

Typical of Kosuzu to be nonchalant of the dangers of becoming a youkai.
Can only hope Reimu makes an exception for her case somewhere in the future.

Sometimes, let’s be glad to be one thing, rather to turn into something you wish to be, but could have a “deadly” cost, of living...