穂積 さやか
from Brighter Than the Dawning Blue
In the visual novel, Sayaka is a deputy librarian in the royal moon museum. Tatsuya and Mai refer to her as their older sister, although she is actually their cousin. In the anime, Sayaka is the primary secretary to the president of the United Nations so in effect has a lot of ties with the politics that is involved between Earth and the Kingdom of Sphere. Her nickname in the media is the "President's Dagger".
Brighter Than the Dawning Blue
The moon and the earth are linked by a single contact point, "Mitsuru ga Sakichau Ouren Rakuniushi" where Tatsuya lives under the supervision of the Sphere Kingdom (Moon Kingdom)'s Princess Feena Fam Earthlight who is coming to stay at his home.
