Just from physics point of view, the nitrogen Henry’s law constant in water (don’t know the value in the blood) is 1600 atm / (mol/litre) at 25C. For discussion point of view, let’s assume the nitrogen Henry’s Law constant in the water is the same as in the blood. Then nitrogen solubility in the blood at the surface would be about 13.8 ppm (0.79 x 28 / 1600 / 1000). At 9 m depth with EAN60 the amount of soluble nitrogen in the blood would be 13.3 ppm, still below saturation. As you ascend to the surface, you will load less nitrogen (5.52 ppm). At any point during the dive you have not pushed your body beyond the maximum nitrogen loading that your body can take. So, how would the bubbles form if all of the dissolved nitrogen is still below saturation? I’m confused. Am I missing something?
With the OPs hypothetical dive, the diver is breathing gas with a similar (slightly lower) PPN2 as in surface air, so no ongassing (slight offgassing at 30 FSW, actually, 0.76<0.79, until he reaches equilibrium again). In the steady state, the compartments are saturated, first the fast ones and then the slow ones.
But as you ascend, ambient pressure decreases, so your PPN2 in your inspired gas is now lower than that, creating an offgassing gradient between p(tis) and p(insp). Compartment saturation isn't an absolute number, it's relative to ambient pressure. If you take a saturated tissue compartment and drop the ambient pressure, you create a PPN2 gradient and offgass. Ascending makes the tissue compartments supersaturated, until they reach a new equilibrium.