Kaiju
A large unidentified object that crash-landed in the city and destroyed everything in its path.
In the 2065 ruins, Natsuno Minami witnesses a giant, four-legged machine that looks just like the weapons that the aliens used in the sci-fi classic, "The War of the Worlds."
The hologram that appeared inside the 2025 remains of the kaiju stated the following: Shikishima Interstellar Development Division Terraforming Project #8834, 3rd phase, Surface Construction and Modification, Colossal Autonomous Heavy Machinery, D series, D-800, Giant Moler, Surface Excavation Unit.
Deimos is the generic name for kaiju, and there are many types. Some models can be as large as entire buildings, while others are about the size of a large car.
The kaiju are the result of a program created by Ryoko Shinonome of 2188, created to attack the simulated world by utilizing the simulation game, "Deimos." She had done this to make sure humanity would not survive to see the new world.