This ending is similar to the Rooftop Ending with a slight difference, but still easy to get.
It is virtually the same as the rooftop ending, except as Sabitsuki is outside, a gas-mask maid will appear. The screen then fades to black and the maid is shown carrying Sabitsuki away.
Drop all your effects into the computer (use the computer while in .flow, then walk to the center star and confirm). You will be sent back to the real world, just take the door to the rooftop.