Long ago, there was king of all demons, Lord Dante. As king of the demons he forcefully merged the earth realm and demon realm as one. Doing so cause massive catastrophe. With his corrupted mind, he allowed demons to attack Osaka Japan and rule over what's left of it afterwards. After taking over Osaka, Kyoto, Nagoya, Nara, Hiroshima and more, only 4 cities were able to fend off against the demons