2D visualization of radius and enclosed mass at four snapshots for a 12 M_⊙ star from single-star model Set I, with an initial accretion rate of 1.0 × 10⁻³ M_⊙ yr⁻¹. The snapshots span evolution phases before mass transfer (MT), during MT, during thermal relaxation (TR), and after restoring TE. The reference time is t₀ = 10.06 Myr. We ignore deviations from spherical symmetry due to critical rotation and use the averaged radius in the X–Y plane. The color scale denotes enclosed mass, with two distinct color maps applied below and above 12 M_⊙ to differentiate the original stellar mass from the accreted mass. Hatched regions in panels b–d highlight the accreted layers. The thin horizontal dashed line marks the stellar radius at t₀, and the current stellar radius is labeled in each panel.