I have made natto and also within the last month. You use store bought natto to inoculate your soybeans. Store bought come frozen from Japan and go for about $2 for a 3 pack.
Here are the best natto making instructions I have seen. I used them last time. https://www.youtube.com/watch?v=e0hjr6clnHM You must soak and then steam the soybeans. Boiling them does not work.....
He also has a regular old website with more details and comments.
Good for you!
Thank you for sharing a good homemade version.
I wish natto didn’t have so many carbs, though.