162173 Ryugu, the target of Hayabusa2, is a spinning top-shaped asteroid. Observations by Optical Navigation Camera onboard Hayabusa2 have shown that the western side of this asteroid possesses a smooth surface and a sharp equatorial ridge, compared to the other side. Here, we propose that a rotationally-driven deformation process generated the western bulge. Our structural model shows that Ryugu is structurally intact in the subsurface region of the western region while other regions are sensitive to structural failure when the spin period is shorter than 3.75 h, which is the critical spin limit that the failure model becomes global. We infer that this variation is indicative of the deformation process that occurred in the past, and the western bulge is more relaxed structurally than the other region. Our dynamics analysis also implies that this deformation process might occur at a spin period between 3.5 h and 3.0 h, providing the cohesive strength ranging between 4 Pa and 10 Pa.