Asthma and COPD are significant respiratory diseases that can coexist, referred to as Asthma-COPD Overlap Syndrome (ACOS). Patients with ACOS experience more severe clinical outcomes, including rapid decline in lung function, increased symptom burden, and reduced quality of life. Pulmonary rehabilitation-particularly breathing exercises-is a core non-pharmacological intervention recommended for this patient group. In recent years, video game-based applications have emerged as innovative tools that enhance motivation and participation in exercise programs. However, studies investigating the effects of video game-based breathing exercises in ACOS patients are extremely limited. Additionally, although dysfunctional breathing patterns are common in this group, few studies have addressed targeted interventions. The objective of the present study is to evaluate the effects of video game-based breathing exercises on dysfunctional breathing in ACOS patients.