Wow! Looks like The Mourning Children: Nagiko and the Girls Wearing Tsurubami Black is not available on any streaming services in the world!

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Kyoto during the Heian period (the 10th century) in Japan. Tens of thousands dead, gutters filled with corpses, children abandoned in the mountains, and groups of wild dogs vigilantly watching outside the city. The elegant image of the Heian period has been shown in many literary and artistic works. However, Katabuchi's new work takes us back to Kyoto a thousand years ago, when the city was shrouded in darkness due to repeated epidemics of plague.