I'm a total amateur, but here's what I did:

1. Soak 1.5 lbs beans for 6 hours in water with a little baking soda
2. Change water halfway through
3. Preheat immersion circulator/sous vide chamber to 110 F
4. Pressure steam for 20 minutes
5. Spread into wide flat container
6. Stir old nattō into 1/2 cup water, mix evenly into beans
7. Lay plastic wrap snugly against beans, poke many holes
8. Cover tightly with tin foil, poke a couple holes around edges
9. Poke corded probe thermometer into center from edge
10. Float in immersion circulator chamber for approximately 20 hours

The temperature in the beans generally kept about 2 degrees less than the chamber. I think we want the early fermentation to happen at 108 F and then cool to 100 F, so I tried to keep adjusting it based on that. Anyway, the result was pretty tasty!! The bacteria seem to take well to black-eyed peas. Might have been a little less stringy than "normal", but still delicious!