Bundled with the limited edition 12th manga volume.

Miyako Arata is newly assigned to the Shinjuku Ward Nocturnal Community Relations Division. Each of Tokyo's 23 wards has one such department, established to mitigate paranormal and occult-related events. Arata's special skill is the understanding of non-human speech, and the story begins with him encountering a youkai at Shinjuku Imperial Gardens who refers to him as the legendary Heian-era exorcist, Abe no Seimei.

(Source: Mayonaka No Occult Wikia)