Lightly rinse the kombu and place in a small bowl along with the meyer lemon juice, shoyu, rice vinegar, and mirin. Cover and let sit for at least a few hours, but preferably overnight.
For a vegetarian ponzu, stop here. Otherwise add the bonito flakes, let sit for a few minutes and strain. (If you want extra smoky ponzu, you can add the bonito in step 1).
Enjoy ponzu tossed with soba noodles, or as a dipping sauce with lettuce wraps or summer rolls. Stored in the refrigerator, it'll keep for at least a few months.
Recipe by Love and Lemons at https://www.loveandlemons.com/meyer-lemo-ponzu/