I know it sounds entirely impossible--a guardian of nature belonging to a faction of destruction and decay?--but I'm determined to make this work. I think it could be great, and in an infinitely infinite multiverse, it must be possible.
The easy way would just be "Death is a part of nature, so therefore destruction rules!" but I'd like to come up with something a bit more contemplative than that. What've you folks got?
If all else fails, a cleric might do, as well, taking Decay, Destruction, and so on for domains.
All shall fade. I see it in the grasslands, slowly dying from the changing climate. I see it in the woodlands, which fall to the progress of empires which shall themselves fall. I see it in the greatest mountains, which erode away ever so slowly, until after a thousand thousand years even they will be reduced to dust.
As a guardian of nature, it is futile for me to attempt to halt nature's course.
But I can help the world go gently into its eventual end.