Ed:

If they were similar to Great Blue Heron, that would have to be Gray Heron,
which is definitely the most numerous heron species in most parts of n.e.
Asia, including Japan. I noticed that Western Reef-Heron is more of a
species of offshore rocks and islets, not inland sites, and the dark form is
most frequent, at least where I went.

Scott Atkinson
Lake Stevens
mail to: scottratkinson at hotmail.com