These are Japanese winterberry flowers (Ilex serrata). Despite their cute smallness, i.e., 3 - 4 mm in diameter, however, the Japanese winterberry is known more for its red fruits produced from September to December. These flowers remind me of longstalk holly flowers, which makes sense. They're both in the Ilex or holly genus.
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| Japanese winterberry (Ilex serrata) ウメモドキ（梅擬） |
