Mekabu-chan (Shadowside)

Rhyth is a Shadowside Yo-kai of the Uwanosora tribe.

Specifically, this is the appearance of Rhyth for the Shadowside series, 30 years after the original series.

Biology
In her Lightside form, Rhyth looks like her original counterpart, but smaller and thinner.

In her Shadowside form, Rhyth is taller and has long seaweed hair.