Background <p>Hikikomori is a multidimensional psychosocial phenomenon characterized by prolonged and severe social withdrawal, often accompanied by significant functional impairment. Although initially described within the Japanese sociocultural context, accumulating evidence suggests that hikikomori represents a global mental health concern. A diminished sense of belonging has been identified as a core feature associated with hikikomori tendencies; however, the psychosocial mechanisms underlying this relationship remain insufficiently understood. This study aimed to examine the association between hikikomori tendencies and sense of belonging among university students, and to investigate the predictive roles of problematic internet use, interpersonal sensitivity, psychiatric symptoms, and hopelessness within a comprehensive multivariate framework.</p> Methods <p>This cross-sectional study was conducted with 429 university students recruited from a public university in Türkiye. Data were collected using online self-report questionnaires, including the Hikikomori Questionnaire-25 (HQ-25), General Belongingness Scale (GBS), Online Cognition Scale (OCS), Beck Hopelessness Scale (BHS), and Symptom Checklist-90-Revised (SCL-90-R). Pearson correlation analyses, multiple regression analyses, and Structural Equation Modelling (SEM) were employed to examine direct and indirect relationships among variables. Age and gender were controlled as potential confounders.</p> Results <p>The tendency toward hikikomori was significantly negatively associated with perceived acceptance/inclusion and positively associated with perceived rejection/exclusion. Problematic internet use, particularly the online social comfort dimension, emerged as a significant predictor of increased tendencies toward hikikomori and a reduced sense of belonging. Hopelessness was identified as a strong and consistent predictor of both hikikomori tendency and perceived social rejection. SEM analyses indicated that interpersonal sensitivity had a direct effect on hikikomori tendency, while anxiety, depression, and psychoticism exerted indirect effects through interpersonal sensitivity. The final model demonstrated good fit and explained a substantial proportion of variance in hikikomori tendency and belongingness outcomes.</p> Conclusions <p>The findings provide empirical evidence that the tendency toward hikikomori is closely linked to a diminished sense of belonging and is shaped by a complex interplay among problematic internet use, interpersonal sensitivity, and hopelessness. While online environments may offer temporary social comfort, excessive reliance on virtual socialization appears to reinforce social withdrawal and feelings of exclusion. Targeting interpersonal sensitivity and hopelessness may be particularly important for developing effective interventions to reduce social withdrawal and promote social reintegration among university students.</p>