Relatives are crucial partners in institutional long-term care, but their complex experiences often go unrecognised. This meta-synthesis aims to explore the multifaceted process of "being relative" from their perspective, transcending functional roles to reveal their full personhood. The study uses the metaphor of the "institutional mask" to challenge the reductionist view of relatives as merely functional caregivers. We argue that relatives navigate a complex, dynamic process of adaptation and meaning-making behind this mask. Following the PRISMA guidelines, we systematically searched databases (MEDLINE, CINAHL, Scopus, Web of Science, Psyndex) for qualitative studies on relatives' experiences in institutional long-term care. Using a reflexive thematic analysis, we conducted a meta-synthesis of 59 studies from seven countries. Our analysis revealed four meta-themes, forming a cyclical "Being relative" model. The first theme, Managing Ambiguity, describes the relatives' continuous process of balancing contradictory emotions, experiencing vulnerability, and finding acceptance and appreciation. The second, Fluid and Overlapping Roles, highlights the shifting between active advocacy and care provision, strategic presence and observation, and coordinating and mediating functions. Third, Dynamic Relationship Development, illustrates the evolution of connections with staff through recognition and relationship challenges. Finally, Negotiating Care Responsibility explains the ongoing adaptation of involvement patterns and balancing care obligations. These themes form a cyclical model illustrating how relatives continuously navigate between institutional expectations and authentic experiences. Our cyclical model challenges reductionist approaches and emphasises the need for person-centred care that recognises relatives as whole persons with complex identities and emotional needs, looking behind the institutional mask to see the individual.