Neat concept to find the little oil pockets via seismic laser reflections. but that function is such a minor side thing that the reflection theme is barely used. also the monitor in the bottom left can be in the way. would be nice if you could turn it on and off.
the aiming honestly sux. you can only shoot in the 4 directions + diagonal. which makes it hard to hit enemies that arent perfectly in line and since the aiming also makes you move its even easier to miss you shots. its nice that you heal from consuming the oil. but since enemies are also defeated by walking into them and are always in the oil pockets you can just facetank through them and immediately heal the damage. it would be better if enemies werent defeated by contact and instead of aiming via movement using mouse aim. also using mouse buttons to dig and shoot instead of "j" and "k". that way the shooting wouldnt be so frustrating and you wouldnt just be able to facetank your way through.
the music is way too loud and quite monotonous. since you directly start the game you have no options to adjust volume. also speaking of starting right away: the explanation pictures rush through too fast. not everyone is a fast reader. making it only advance through button press (or click) would be better.
the sprites are cute. but otherwise the visuals are quite monotonous. after a certain depth the oil becomes invisible. i could still hear the sound of yuuma absorbing oil and she was healed but i couldnt see it.
also: windows defender recognizes your game as a risk because it isnt signed... people lacking technical knowledge could get scared off by that (also they might not know that you have to click on "additional information" to make the "execute anyway" button appear, so they might think its unplayable...). so sign your programs...