Both Fujifilm X-E2S and Olympus E-M10 MIII have 16.0 MP resolution sensors but Fujifilm X-E2S's sensor is APS-C (23.6 x 15.6 mm ) and Olympus E-M10 MIII's sensor is Four Thirds (17.4 x 13 mm ).
Since Fujifilm X-E2S's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Olympus E-M10 MIII.
Another difference between these two cameras is that Fujifilm X-E2S's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the X-E2S and E-M10 MIII sensor size comparison.
As seen above, Fujifilm X-E2S has a 1.6x Larger sensor area than Olympus E-M10 MIII. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.