I'd like to add to this: in Gensokyo, almost all the humans are descendents of exorcists and magicians sent to fight the youkai, before getting sealed in with them. As a result, many are possessed of spiritual strength, and are capable of fighting against youkai. Reimu and Marisa are the most noteworthy examples, but I see no reason why there couldn't be other, less skilled exorcists in Gensokyo.
I'd like to add to this: in Gensokyo, almost all the humans are descendents of exorcists and magicians sent to fight the youkai, before getting sealed in with them. As a result, many are possessed of spiritual strength, and are capable of fighting against youkai. Reimu and Marisa are the most noteworthy examples, but I see no reason why there couldn't be other, less skilled exorcists in Gensokyo.
While we know that there are some exterminators in the village, i think it is more because they trained for it, than because of their ancestors. Marisa, for example, would have no power at all without giving all herself in magic research, and even low-level youkai and some fairies like Cirno are considered to be dangerous enough to normal humans that is suggested to avoid them. Sure, there are naturally-gifted humans like Reimu or Sakuya, but they are probably really rare.
However,once you know its true form...she becomes a youkai,a youkai with "unidentified form".Nue,It has the power to take an unknown form and eat at our fear.----What is he...?----Come everyone,frail enough to slay with human strength.