Since the era changed from Edo to Meiji, Japan has been changing rapidly with the current government's policy of modernization. Kyoto where Expo was being held.
The government issued licenses to monsters that lived with humans. There was a company that arrested unregistered monsters to keep the peace. The name of the company is "Kido Shinsengumi Co. Ltd."
Meanwhile, a young guy came back to Kyoto from Shanghai with his monster buddy, Nekomaru. He was Sakamoto Ryunosuke, the son of Sakamoto Ryoma.