Five years ago, in Asakusa, Robin, Haruki and his racer sister Kiriko had spent their days happily living in an orphanage.

Maru and Kiruko are on the hunt for the Immortal Order. On the way, they stay at a hotel run by a girl named Totori. Dumping their bags and searching for safe drinking water, they stumble upon a badly injured man.

After killing the Man-Eaters, Maru and Kiruko finally meet Dr. Usami. He asks something difficult of them, and leads them both to a room where a horrifying scene awaits.

Maru and Kiruko decide to head to the Ibaraki facility of the Takahara Academy. Since it's on the way, they agree to help Juichi confirm whether his baby is still alive. Arriving at the Walled Town, the situation is very different to what was expected.