The dark-haired bishounen is Sakon Tachibana, a puppeteer, and the other is Ukon, his favorite puppet and best friend. Sakon is the (only) grandson of Saemon Tachibana, a national treasure of Japan famous for his manipulation of Bunraku puppets. Ukon is a child doll puppet made in the early Meiji era by the famous female dollmaker Unosuke. Together they run into murders and solve them.
(Source: AnimeNfo)
— Description from AniList community (anilist.co).
