Contact infrastructure and the wall: how international students' host-world affiliation is produced and bounded in Japan

International students' host-language use and social integration are usually explained by proficiency or national origin. This study argues that host-world affiliation is produced by contact infrastructure: the repeated, low-stakes occasions for contact that institutions and living arrangements provide. A wall of host reticence, produced by both sides, bounds it. The COVID-era withdrawal of these occasions is read as a revelatory rupture that made them visible by removing them. An explanatory sequential mixed-methods design drew on a survey of international students (N = 176) and 39 interviews with 40 international students at one national research university in Japan. Four domestic students were interviewed as a labelled host-side comparison. Choice of the Japanese survey form indexed host-language orientation. Origin dominated that choice, while contact-type indicators were weak. The interviews explain the pattern. Affiliation followed the occasions for contact. When the pandemic removed them, reported loss largely tracked how much a student's world had rested on them. One of the 40 cases ran against this. Host and international students placed the campus boundary in the same location: in reticence and missing shared ground, not hostility. Participants described the wider society, by contrast, as hostile through housing, policing, and hiring. Nationality worked as a marker read from outside, not as a driver of conduct. The lever for belonging is the design of contact occasions, not language instruction alone.