Japanese laws regading the 'height' of your car relate to the chassis and what hangs off it from an 'engineering' perspective ( exhaust, etc ) - so, as a result, they design body kits which make the car 'look' really low. a la kenstyle, Galia, etc. the car isnt lowered, the body kit is. Nightmare. And I completely empathise with it!
'Bold world' (Japanese company) have an air suspension kit (more than one actually) so if you're serious about it I'd chase them up first up.