Aoi Tsubaki (voiced by Nao Toyama) seems to be just an ordinary sophomore girl in college, but she actually inherited the power to see monsters from her grandfather. After her grandfather passed away, Aoi was suddenly summoned to a hotel called "Tenjinya" one day. This hotel is located in a hidden world where monsters gather. It turns out that Aoi's grandfather signed a huge debt before his death. He had no choice but to use Aoi to pay off the debt and promised to marry Aoi to the big boss of Tenjinya (voiced by Katsuyuki Konishi). However, Aoi was unwilling to go against her own wishes, so she decided to stay in Tenjinya and work part-time to pay off the debt. Ginji (voiced by Shunichi Toki), a perfectionist, Akatsuki (voiced by Yuuma Uchida), who is impulsive and rude but works hard every day, and Yuki Onna (voiced by Ai Kakuma), who looks indifferent but has a fiery heart, together with these monsters, Aoi's daily life begins.