I can’t remember the title, but I think I know the one you’re talking about. In case more details will help someone else remember the title:
-the detective and the brother are actually twins. The twin brother is a scholar specializing in folklore. Their dad is high up in the police dept, like the chief or commissioner
-the first volume is about a mystery in a secluded town, and it also involve twins who are basically being held captive/coerced
-the next arc was about as a small town that deified a mermaid

Hello! I am looking for a bl
The story follows a police/detective who always wears sunglasses and he drags his brother who is an author to help him work a case in a remote village. This village has reports of people disappearing near it and it is because they sacrifice them to a set of twins. One is trapped in a cage because of his eyes and the other has sex with strangers because of a ritual. Both brothers fall in love with each twin and now it is the second volume where the twin with special eyes gets kidnapped to be apart of another ritual.
Does anyone know its name? I have been looking and have not found it yet. It is a pretty good story, so I would like to finish it.