A Hierarchical City (階層都市 Kaisō Toshi) is a term used to describe cities that were built after the Great Dark War by the World Void Information Controlling Organization. There are 23 hierarchical cities known thus far.
After the Great Dark War, which left a large amount of hazardous Magic Element that covered the world, a lot of humans and animals became tainted with the Magic Element and died off. Humans were forced to move to high altitude, mountainous areas where concentration of Magic Element is lesser. Hierarchical Cities exist around the world in various regions, and each one is assigned a number. The highest placed Hierarchical City is the first, the lower it is, the higher the number of the city. In each hierarchy are many cities, towns, villages. The upper level contains the Controlling Organization branch office, while the higher layers are reserved for the wealthy, Controlling Organization personnel, and collaborators. The poor, refugees, and other indigenous races live in the lower layers.
Weather in the cities is maintained by the Environment Maintenance Device, and they are also surrounded by a special barrier. Its properties are unknown, but according to Hakumen, it's similar to the Ishana's barrier.
People travel between cities by aircrafts, which are monitored by the Controlling Organization. Some exceptions are Ikaruga Federation cities, as they're so close to each other that people can travel between them by trains safely.
Each of the Hierarchical Cities have a Kiln deep within.
- The 0th City of Izanagi (第零都市「イザナギ」 Dai-Zero Toshi "Izanagi")
- The 1st Hierarchical City "Ōkoto" (第一階層都市「オオコト」 Dai-Ichi Kaisō Toshi "Ōkoto")
- The 2nd Hierarchical City "Iwatsuchi" (第二階層都市「イワツチ」 Dai-Ni Kaisō Toshi "Iwatsuchi")
- The 3rd Hierarchical City "Iwasu" (第三階層都市「イワス」 Dai-San Kaisō Toshi "Iwasu")
- The 4th Hierarchical City "Naobi" (第四階層都市「ナオビ」 Dai-Yon Kaisō Toshi "Naobi")
- Ikaruga Union of Hierarchical Cities (連合階層都市イカルガ Rengō Kaisō Toshi Ikaruga), originally known as the Ikaruga Federation (イカルガ連邦 Ikaruga Renpō)
- The 5th Hierarchical City "Ibukido" (第五階層都市「イブキド」 Dai-Go Kaisō Toshi "Ibukido")
- The 6th Hierarchical City "Yabiko" (第六階層都市「ヤビコ」 Dai-Roku Kaisō Toshi "Yabiko")
- The 7th Hierarchical City "Kazamotsu" (第七階層都市「カザモツ」 Dai-Nana Kaisō Toshi "Kazamotsu")
- The 8th Hierarchical City "Wadatsumi" (第八階層都市「ワダツミ」 Dai-Hachi Kaisō Toshi "Wadatsumi")
- The 9th Hierarchical City "Akitsu-Kō" (第九階層都市「アキツ―甲」 Dai-Kyū Kaisō Toshi "Akitsu-Kō")
- The 10th Hierarchical City "Akitsu-Otsu" (第十階層都市「アキツ―乙」 Dai-Jū Kaisō Toshi "Akitsu-Otsu")
- Izumo Region (イズモ地方 Izumo Chihō)
- The 11th Hierarchical City "Shinatsu" (第十一階層都市「シナツ」 Dai-Jūichi Kaisō Toshi "Shinatsu")
- The 12th Hierarchical City "Kukunochi" (第十二階層都市「ククノチ」 Dai-Jūni Kaisō Toshi "Kukunochi")
- The 13th Hierarchical City "Kagutsuchi" (第十三階層都市「カグツチ」 Dai-Jūsan Kaisō Toshi "Kagutsuchi")
- The 14th Hierarchical City "Nozuchi" (第十四階層都市「ノヅチ」 Dai-Jūyōn Kaisō Toshi "Nozuchi")
- The 15th Hierarchical City "Torifune" (第十五階層都市「トリフネ」 Dai-Jūgo Kaisō Toshi "Torifune")
- The 16th Hierarchical City "Ōgetsu" (第十六階層都市「オオゲツ」 Dai-Jūroku Kaisō Toshi "Ōgetsu")
- The 17th Hierarchical City "Yamatsumi" (第十七階層都市「ヤマツミ」 Dai-Jūnana Kaisō Toshi "Yamatsumi")
- The 18th Hierarchical City "Kanayama-Yamabiko" (第十八階層都市「カナヤマ-ヤマビコ」 Dai-Jūhachi Kaisō Toshi "Kanayama-Yamabiko")
- The 19th Hierarchical City "Kanayama-Yamabime" (第十九階層都市「カナヤマ-ヤマビメ」 Dai-Jūkyū Kaisō Toshi "Kanayama-Yamabime")
- The 20th Hierarchical City "Haniyasu-Yasubiko" (第二十階層都市「ハニヤス-ヤスビコ」 Dai-Nijū Kaisō Toshi "Haniyasu-Yasubiko")
- The 21st Hierarchical City "Haniyasu-Yasubime" (第二十一階層都市「ハニヤス-ヤスビメ」 Dai-Nijūichi Kaisō Toshi "Haniyasu-Yasubime")
- The 22nd Hierarchical City "Mizuha" (第二十二階層都市「ミズハ」 Dai-Nijūni Kaisō Toshi "Mizuha")
- The 23rd Hierarchical City "Wakumusubi" (第二十三階層都市「ワクムスビ」 Dai-Nijūsan Kaisō Toshi "Wakumusubi")