...it is highly plausible for nature to be changed as well.
Therefore, if a fairy is to undergo a change...
The fairies are said to reside within each of nature's phenomenons. (From <a href=http://en.touhouwiki.net/wiki/Perfect_Memento_in_Strict_Sense>Perfect Memento in Strict Sense</a>)
Within the wind and rain... within the grass and flowers... along with the seasons...
Fairies are personifications of nature in Gensoukyo.