This study analyzes changes in the usage rate of the Japanese honorific expression nasaru, its distribution by conjugational form, and its contextual usage, along with speaker characteristics, since the 2000s. The analysis is based on data from the Budget Committee of the House of Representatives in the National Diet Proceedings from 1947 to 2025 across nine time periods. The findings are as follows.
ⅰ) The usage rate of nasaru peaked in the 1970s but has since declined, reaching a very low level by the 2020s. The differences observed across the various time periods were statistically significant, confirming a long-term downward trend.
ⅱ）In terms of conjugational forms, the attributive form, te-form, ta-form, and polite form accounted for most occurrences. In contrast, the continuative form, conditional form, and irrealis form were nearly obsolete, appearing only in a few cases. Among these, the te-form and ta-form maintained the highest frequency even after the 2000s, indicating that they function as the central forms of nasaru in recent usage.
ⅲ）The te-form and ta-form since the 2000s, where the speaker directly references the actions or statements of the interlocutor. These forms can be understood as both redressive acts that help mitigate face-threatening situations, as described by Brown and Levinson (1987), and as linguistic practices that maintain institutional relationships in line with Ide’s (2006) concept of wakimae, meaning “discernment.” ⅳ）A very small number of recent examples of the irrealis form nasara have been identified. Its usage seems to have shifted from direct criticism and pursuit, as seen in earlier periods, to contexts that involve considerations and requests.
ⅴ）An analysis of speakers who used nasaru after the 2000s revealed that its usage was concentrated among a limited number of speakers. This suggests that the continued use of nasaru may be influenced not only by formal and contextual factors but also, to some extent, by the individual linguistic habits of specific speakers.