Draw big circles and fill the gaps with small ones. My condolences if you have this in Suika Game.

Rough and widen the circles up with the warp tool.

Make a copy of the layer, change the color of the drawing, offset it a bit, put behind the original then change blending mode to multiply. What a multitask.

Gaussian blur the shadows

Put seashells, sea glass, etc. on a new layer.

Put lights and flow on a new layer.