Tonkatsu ramen broth is a rich, flavorful broth like none you can buy. The long cooking time seems like a lot of work, but it is SO WORTH IT! If you're going to be home anyway, why not throw this in the pressure cooker.
I have a huge pressure cooker. You may need to cut the recipe in half for your pressure cooker.
Place bones in a large pan and cover with cold water. My pressure cooker's pan can go on the stovetop so I just use that pan.
Bring to a rolling boil over medium high heat. Allow to cook at a rolling boil for 5 minutes. A scum will form on the top. Remove from heat.
This seems so counterintuitive, but DRAIN all of the water off and rinse the bones under cold water.
Place bones, remaining ingredients and enough water to meet fill line of pressure cooker.
Pressure cook on high for 10 hours. My pressure cooker has a 2 hour limit so I have to put it through 5 cycles (without releasing the pressure in between).
Check about half way through to make sure you haven't lost too much liquid. Top off the water if necessary to keep it at the fill line.
When the broth has cooked long enough, it should be thick and rich looking - not clear like canned chicken stock.
Remove large chunks of bone, veggies with tongs or a slotted spoon and discard. Drain the remaining stock into another large container* through a fine sieve.
*Don't accidentally pour it down the drain! #AsMeHowIKnow
Note: You could also just boil it at a ROLLING BOIL for 12 hours in a large stock pot with a tight fitting lid if you don't have a big enough pressure cooker. Make sure to leave plenty of room for bubbling as the rolling boil is important. You won't get the right result with the lower simmer you might use for chicken stock. Watch the water level REALLY closely to make sure it doesn't go dry and burn.