Combine the Bamboo Shoots (1/2 cup), Water (2 cup), Teriyaki Sauce (1/2 cup) and Mirin (1/4 cup) in a medium saucepan.
Bring to a boil over medium-high heat, add the Bonito Flakes (1 handful), then reduce the heat and simmer for 25 minutes.
Remove from the heat and let cool. Transfer the menma and its seasoning liquid into an airtight container and refrigerate overnight before using.
Store in the container with the liquid in the refrigerator for up to a week.