Hikikomori is commonly defined as a state that continues for 6 months or longer, in which an individual remains at home on most days, does not work or attend school, and has almost no interaction with people outside the home, aside from occasional short solitary outings (Nonaka et al., 2022; Saito, 2010). This condition was recently included in the DSM-5-TR (American Psychiatric Association, 2022) as a cultural concept of distress, and has since attracted growing international attention (Cai et al., 2023; Pupi et al., 2025; Zhang et al., 2025).

Initially noted mainly in Japan and other East Asian regions, hikikomori has been documented across a wide range of cultural contexts, and the number of international studies emphasising its mental health risks has risen steadily in recent years. For example, Nonaka et al. (2025a) found that relative to non-hikikomori controls, individuals with hikikomori exhibited significantly higher levels of internalising symptoms, externalising symptoms, and thought disorder features, with effect sizes in the moderate to large range. Moreover, when hikikomori co-occurred with established psychiatric disorders, the symptom severity was often higher. Patients with major depression (Teo et al., 2020), social anxiety disorder (Nagata et al., 2013), or autism spectrum disorder (Yamada et al., 2023) who met the criteria for hikikomori showed more severe clinical presentations than their counterparts without hikikomori, underscoring the need for early hikikomori screening.

Operant conditioning provides a functional framework for analysing the maintenance of hikikomori behaviours. Positive reinforcement is the process by which presentation or magnification of a stimulus increases the rate of the preceding behaviour. By contrast, negative reinforcement increases the rate by terminating or attenuating a stimulus. Drawing on the functional-analysis classification of Iwata et al. (2013), types of reinforcement can be classified as social (social-positive or social-negative) or automatic (automatic-positive or automatic-negative) according to the presence or absence of others’ involvement. Using this framework, the recently developed Hikikomori Functional Assessment Scale (HFAS; Nonaka et al., 2025b) identifies three empirically supported functions: social negative reinforcement (e.g. avoiding interpersonal demands), intrapersonal positive reinforcement (e.g. pursuing enjoyable solitary activities), and intrapersonal negative reinforcement (e.g. relieving internal distress). In a large validation sample, social negative reinforcement showed the strongest association with higher depression, poorer adaptive behaviour, and lower quality of life, indicating that it is a sensitive marker for early intervention. Because the HFAS is a brief self-report tool, it can be administered without face-to-face contact, which many individuals with hikikomori actively avoid, making it a practical screening tool before multimethod workup in research and clinical settings.

A previous study (Nonaka et al., 2025b) acknowledged a limitation: the scale has not yet been compared with ratings from clinician interviews. Furthermore, questions remain about whether the HFAS is sensitive to within-person changes and whether such changes co-vary with outcomes. To address these gaps, the present study preliminarily examined the consistency between the HFAS self-ratings and ratings from interviewers masked to the test scores. Consistency was discussed at two retrospectively defined time points, the participant-identified peak period of hikikomori (Peak) and the assessment time (Current). Additionally, we explored whether self-reported changes in perceived functions from Peak to Current tracked parallel changes in psychological and behavioural outcomes.