If nothing else, Earwig shows that, if it wants to, Ghibli can make a CG anime that looks good and still looks like Ghibli.
Interest is sky-high whenever Ghibli announces a new project, but audience expectations for Earwig hadn’t reached quite the same altitude.
Japanese all-CG productions don’t have the best reputation, often due to attempts to force-fit pseudo-hand-drawn elements into the characters’ movement.
Looks like you’ll have to read the book, because the anime doesn’t tell you anything other than that they exist.
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Earwig and the Witch [Official English Trailer, GKIDS]