Olympus SZ-31MR iHS has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Dual TruePic V processor. On the other hand, Olympus E-M1 II has a
20.0MP Four Thirds (17.4 x 13 mm ) sized CMOS sensor and features TruePic VIII processor.
One other difference between these two cameras that is worth mentioning is that Olympus E-M1 II's sensor doesn't have an 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 moiré occurring in certain scenes.
Below you can see the SZ-31MR iHS and E-M1 II sensor size comparison.
As seen above, Olympus E-M1 II has a 8.1x Larger sensor area than Olympus SZ-31MR iHS. 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.