The Japanese Ministry of Defense has an anti-paranormal special forces group called the Paranormal Disaster Countermeasure Headquarters. They're the ones responsible to protect Japanese soil and its people from supernatural and paranormal events. However, things didn't go so well in one of their missions, which leads to intervention by the Ministry of Enviroment's Supernatural Disaster Countermeasures Division after the PDCH has sustained large numbers of casualties battling demons.
As a child, Raku Ichijo made a secret promise with his childhood sweetheart, keeping a pendant as a memento while his love took the key. He dreams of one day meeting his past love, but years later, reality smashes his hopes when Chitoge Kirisaki accidentally knees him in the face. Though Raku's a normal high schooler, his family heads the notorious yakuza gang the Shuei-Gumi faction. And he's dragged into family affairs when he's forced into a relationship with Chitoge, the daughter of a rival gang's boss.