Leader of the secret organization called the Millennium Thieves, organization which oppose La Metal.

Anime TV Series
She uses a gloomy old mansion as a hideout. She kept her identity hidden by wearing a mask, black trench coat, and even used a strange mechanical voice. In the anime TV series, when she finally revealed her true self, she is somewhat identical to Yayoi, her younger sister who is to be the next Millennial Queen. Prominent differences between those two were the voice and Selen's darker blonde hair.

Anime Movie film & Manga
Yayoi's younger sister. She gets a scar on her face, similar to Emeraldas'. In the Movie film, Selen's appearance looks almost identical to Millennial Queen, except for her brown hair. Selen battles La Metallians to save the earth and unlike in the anime TV series, she dies after being out numbered by enemy aerial units.