Background <p>Wind-induced responses in tall buildings with unconventional geometries remain insufficiently explored, particularly for complex X-shaped plan forms. Limited aerodynamic performance data exist for such configurations, leading to uncertainties in design and safety assessment.</p> Purpose <p>This study aims to evaluate the wind-induced vibration characteristics and dynamic responses of a tall X-shaped plan building and to compare its performance with a setback-modified configuration in order to identify potential benefits and trade-offs.</p> Methods <p>Validated Computational Fluid Dynamics (CFD) simulations were conducted under a reference wind climate. Two geometrical configurations—a prismatic X-shaped building and a setback-modified variant—were analyzed to assess along-wind forces, across-wind forces, and torsional responses under turbulent wind flow.</p> Results <p>The setback-modified configuration demonstrated improved aerodynamic performance, with reductions of approximately 20% in along-wind forces, 15–20% in overturning moments, and more than 25% in torsional moment fluctuations. However, these reductions were accompanied by an increase in across-wind forces, indicating heightened susceptibility to vortex-induced vibrations.</p> Conclusions <p>The results highlight a clear performance trade-off associated with aerodynamic modifications such as setbacks. While these modifications effectively mitigate along-wind and torsional responses, they may intensify across-wind effects. Consequently, supplementary passive damping measures may be necessary. This study provides benchmark data for X-shaped plan buildings and emphasizes the importance of comprehensive aerodynamic assessment beyond simplified design code provisions.</p>