Culinary collaborations are commonplace these days, with chefs flying halfway around the world for one-off events far from their home kitchens. This exciting cross-fertilization of ideas and flavors is also starting to happen in Japan — but rarely, until now, in the field of traditional Japanese cuisine.

A lack of experimentation is understandable in the closed world of Kyoto restaurants and their elaborate, hyper-seasonal kaiseki ryōri (multicourse cuisine). But Tokyo sushi chefs can be just as insular. One exception to this is Toshikatsu Aoki, who took over his family business in Tokyo's Ginza district at the tender age of 29 and over the past two decades has won a strong following for his classic sushi that is relaxed and contemporary.

Last month, Aoki launched the first in a series of collaboration pop-ups named Project Blue Tree at his larger Nishi-Azabu branch, and there are two surprises. The first is that he is offering a full-scale kaiseki menu. The second is that the chef behind his counter is American.