Possessing a deep knowledge of mineralogy, Richard Ranasinghe de Vulpian is a young and handsome British jewelry appraiser who owns a small shop in Japan. One fateful night, Seigi Nakata, a righteous college student, saves him from drunks who were harassing him due to his good looks. Upon learning of Richard's identity, Seigi hires him to appraise a pink sapphire ring that was left behind by his deceased grandmother.

Before long, Seigi becomes a trusted part-timer at Richard's shop. Together, the duo solve various jewel-related requests from diverse clients of different backgrounds. Step by step, they unravel the hidden motives and feelings that lie within the gems in order to understand and empathize with the little stories behind each piece of jewelry.