MUSE continuum-subtracted emission-line images around NGC 5408 X-1 in Hα, [O III] λ5007, Hβ, [S II] λ6716, and He II, together with a two-color image combining Hα and He II. The white bars or cross mark the ULX position. In the Hα panel, the white circle marks the spectral extraction aperture for the entire nebula shown in Figure 4; the corresponding background region lies outside the displayed field. In the [O III] λ5007 panel, the Hα contours are overlaid in cyan, while the dashed circle with a radius of 18 pc marks the displacement of emission peak to the ULX. The Hβ, [S II] λ6716, and He II images are smoothed with a Gaussian kernel of σ = 1 pixel. The arrow points north and has a length of 40 pc (﹩1\mathop{.}\limits^{^{\prime\prime} }72﹩).