<p>Forest bathing, or shinrin-yoku, has gained international recognition as a nature-based intervention for mental health, commonly explained through frameworks such as Attention Restoration Theory, Stress Reduction Theory, and Biophilia Hypothesis. While these models emphasise sensory restoration and physiological recovery, they largely adopt a one-directional, human-centred orientation. This article introduces the Gratitude to Nature (GRAN) Model, a novel conceptual framework re-interpreting forest bathing as a reciprocal, co-regulative relationship with nature. Unlike existing frameworks, the GRAN Model integrates insights from ecological and environmental psychology with cultural worldviews, particularly the Japanese Shinto philosophy of reverence for nature, to explain how gratitude operates as a psychological and relational mechanism of healing. Drawing from cultural traditions where nature is approached with gratitude, the GRAN Model emphasises mutual attunement between humans and the living world. Reciprocity in this model refers to both behavioural expressions (e.g., offering, care, conservation) and psychological states (e.g., gratitude, humility, respect). Rather than extracting benefits from nature, individuals cultivate gratitude that strengthens emotional regulation, prosocial motivation, and ecological awareness. This framework positions gratitude as a mediating process linking nature connection to both personal wellbeing and sustainable behaviour. The GRAN Model expands the theoretical landscape of forest bathing by integrating social, cultural, and relational dimensions into practices of nature connection and well-being. Future empirical work is needed to test this model.</p>