Metis is the mother and second personality of Athena.

Without the full extent of her powers, Metis greatly resembles Athena, but with different colored cloths. She looks like a girl in her early teens with grey-white hair and purple eyes, dressed in a school uniform with a knit cap on her head.

After absorbing Athena, she seemingly ages to her early twenties, and her clothing transforms into a Grecian toga, wearing a crown of flowers on her head, and wielding a scythe (although the colors of her cloths and eyes differ).

Metis is a Snake (Earth Mother Goddess) who swallows Steel, allowing her to steal the power of Steel gods. For example, she was able to wield Ame no Murakumo no Tsurugi after stealing it.
It is suggested that she wields all the powers of her daughter Athena.

(Source: Campione! Wikia)