Fierce karmic flames swept over Hokkaido, and looking out from Umi no Maru, one could only see a sea of bright red.

Umi no Maru was the tenshu pavilion of the Matsumae Clan in the underworld. As a daimyo clan that hadn't been affected during the Sengoku period in the mortal realm, it had continued to maintain a neutral existence even after entering the underworld. As a result, it didn't take part in the conflict between the daimyos and the gods and demons. Thus, Umi no Maru was expanded further and further over time, and at this point, it was virtually taking up the entire central region of Hokkaido.

Tall city walls had been erected on either side of Umi no Maru, and they were entirely constructed from the D-grade material, Spirit Devouring Crystal. The city walls extended as far as the eyes could see, and they gave off a warped, semi-transparent black presentation, much like obsidian. The city walls cut off all paths from Umi no Maru to the southern part of Hokkaido, and the inter-realm mirrors were no more than 10 meters away from the city walls, so cavaliers were unable to charge through the mirrors and siege weapons couldn't be completely erected. As a result, it was known as the northern great wall of the Nipponese Underworld.

The reason why Umi no Maru was so resolute was because Hokkaido neighbored the Cathayan Underworld and...