This Communication

It is the 21st century, and humanity is on the verge of extinction by the mysterious life form "Yperite". However, there are survivors in a top-secret research institute on Yarigatake, a snow-covered mountain in Nagano, Japan. The institute is protected by six immortal girls called "Huntress" who were created at the facility. The story begins when one former soldier, Deluja, appears there.