Wrap firm tofu in two layers of kitchen paper, place on a microwave-safe plate, and microwave at 600W for 1.5 minutes to remove excess water.

Finely chop the onion, place in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 1 minute. Let it cool.

Remove stems from shiso leaves. Reserve 2 leaves for garnish and finely slice the remaining leaves.

In a bowl, mix ground pork, tofu, onion, sliced shiso leaves, and seasoning ingredients until sticky. Divide into two portions and shape into oval patties.

Heat salad oil in a frying pan over medium heat. Add patties and cook until browned. Flip, cover, and steam for 3-4 minutes until cooked through.

Wipe the pan with kitchen paper and add Japanese sauce ingredients. Simmer over medium heat until thickened.