A Servant originating from the Scandinavian Lostbelt.

A "completely different person" compared to the Scáthach from the common history of man, recognized as a god only in the Lostbelt, whose nature is closer to being a queen.

The Nordic Jötun who originated from the Celtic hero Scáthach, the mountain goddess—many of Skaði's (Su-ka-ji) characteristics are revealed.

This side of Skaði should rather be expressed as "the Skaði with some of Scáthach's nature" than dark Scáthach.

(Source: TYPE-MOON Wiki)