Historically, 72% of all the deaths in London are related to dragons, fantastical beings invisible to the majority of the people. While unknown to most, some people have been standing up to these dragons. 
 
Only inhabitants of Reverse London who live in the hidden "reverse" side of London can see the dragons. Even then, only a selected few become qualified enough as witches or wizards to make direct contact with them. 
 
The protagonists of the story are witch duo Noel Niihashi and Ninny Spangcole. They are protection agents for Wing Bind (WB), an organization for dragon conservation and management. Their mission is to protect and manage the dragons within London on behalf of the people. 
 
(Source: Official Site) 

Note: The show was screened in theaters and released online on the same date; the theatrical release combines all three episodes into one.