During Japan’s bubble economy of the late 1980s and early 1990s, immigration surged in response to a severe labor shortage. Japanese filmmakers took notice and made a spate of films about these new, mostly Chinese immigrants. This era culminated in Shunji Iwai’s “Swallowtail Butterfly” (1996), which became the most celebrated and best remembered of the lot and is now being re-released in a restored 4K version.