This takes place in Aperture science. A research facility most well known for the invention of the long fall boots and the portal gun. Yet the Doki Girls were test subjects, and they’ve met ‘their demise’ with GLaDOS. An AI gone kinda rouge to kill.

GLaDOS: “Seriously though, goodbye.” Yuri: “W-wait..!” Sayori: “Spare us we beg.!” Natsuki: “Where’s MC when we need him?” Monika: “Maybe he’s on his way?”