In the Walnut(2001)

Kurumi no Naka

This is the story of Nakai, a filmmaking apprentice, and Tanizaki, the owner of the art gallery In the Walnut. The two of them have been friendly since their days studying art at university, and now their friendship is giving way to a burgeoning relationship. It's hard to get a grip on ordinary Tanizaki, and in reality there's another side to him—a con man side…! Touko Kawai provides a prescription for love in her latest popular series!

(Source: Juné Manga)