"One day at the Decagrammaton operation event..."

"you and some Paranormal Affairs Department teams head to Antarctica. Akeboshi Himari and her team found a strange frequency suspected to be from Decagrammaton. Upon entering the underground room in the SPTF lobby, the figures of three girls appeared right in front of you. One of them is a white-haired girl in a white jacket, with black and yellow-flaming ear covers and orange pupil X and mask. The figure of the girl who appeared before you..."

Yuuka Decagrammaton: cih. "slight expression"