The Case Files of Jeweler Richard (novel series)

The Case Files of Jeweler Richard (宝石商リチャード氏の謎鑑定) is a novel series written by Nanako Tsujimura with cover illustrations by Utako Yukihiro.

Synopsis
Seigi Nakata is a young university student with a great sense of justice who one night saves Richard, a handsome foreigner, from some drunks who annoyed him. When Seigi discovers that Richard is a jeweler, he asks him to please rate him a ring with a somewhat chilling story, one that his grandmother kept secret until she died.