for soft shading use reeeeaaaly low opacity, basically as low as you can get it also color the lineart maybe? if u want the same kind of effect as the ref then that’s what i would do

wooooow syick ref tho

You can use really low opacity to shade the drawing, and you could use unusual colours for the lighting (example:-you can use a yellowish or bluish tone for the lighting in his hair)

is there another way you could get a picture of the refrence? the website is blocked for me