Where is the seed and how do I harvest it? Is it the brown bit once the petals fall off? Tried googling the image of anemone japonica seed with no success.
Japanese anemones form a cottony, fluffy ball where the flowers were and that it is where the seeds will be. When the seeds are ripe, the "cotton" will look like it is dotted with brown grainy bits. Here is a good pic.
Here is a link that might be useful:
I caught a hummingbird collecting the 'fluff' from mine this spring to build a nest! It was neat to see.