Tanaka-san is a legendary hotel man (concierge), and after his death, he became a legend in the underworld. In the underworld, Mei works at the dilapidated Hotel Helheim. It was once a glorious hotel, and one where Mei has many fond memories. One day, Tanaka-san appears, ready to restore the Hotel Helheim to its former success. Mei will become the famous Tanaka-san's assistant, as he works to make Hotel Helheim a top-class underworld hotel!

(Source: MangaHelpers)