i figured out a simple way to achieve a more realistic pupil movement, it's really basic but you must do it to each point in the X Y parameter so see the full effect
step one: choose the Pupil deformer (in the sample, the right eye starts with 右目玉 as a deformer in the EYEBALL group)
step two: go to the point in the parameter you want to change, and squish the pupil in that direction using the blue dot!
with the squished pupil VS without
i guess it doesn't work for every character since eyes are drawn different by every artist, but i started using it on all of my characters and it makes them more expressive