Hiroki conducts research on two subjects in early modern Japanese paintings. One focuses on the stylistic changes in the work of Maruyama Ōkyo, active in eighteenth-century Kyoto, and the way in which they correspond to his relationships with different patrons. The other is the collection history of paintings in the Edo period, especially the collections of the official painters serving the Tokugawa shogunate and of prominent Western collectors such as Ernest F. Fenollosa. 

Prior to attending Harvard, Hiroki received his B.A. and M.A. at the University of Tokyo with a major in Japanese art history. During his time there, he worked as a research assistant at the Tokyo National Museum and Tokyo National Research Institute for Cultural Properties. He later worked at the Museum of Fine Arts, Boston as an Ishibashi Foundation assistant curator of Japanese art.　He has written several papers related to his research and has participated in multiple curatorial projects, performing duties such as editing catalogues and organizing exhibitions.