When the Demon Comes to Kyushu

Starting from September 2030 in the Kyushu calendar, a legendary demon appears in the city. The Kyushu government is secretly cleaning up while searching for the lost secrets; but it seems that there are still some mysterious organizations operating with unknown purposes; ancient inheritances that are usually hidden behind capital are also constantly emerging, and they seem to be trying to find the secret of immortality... In this world full of humans, where do demons come from, and where should humans go?