Add water, kombu, and shiitake to a medium saucepan. Bring to a light simmer for at least 10 minutes.

Add soy sauce, mirin, sugar, wakame, and optional dashi powder. Set aside.

Bring a large saucepan of water to a boil. Add soba noodles, stirring to prevent sticking. Cook 1 minute less than the packet instructions.

Drain, rinse under cold water to remove excess starch, and set aside.

Slice spring onions thinly.

Whisk soy sauce, mirin, onion powder, and ginger powder in a small bowl.

Drain tofu and cut into steaks about 1 cm x 4 cm.

Heat sunflower and sesame oil in a frying pan over medium heat. Add tofu and fry until golden on one side. Flip, add seasoning, and cook until lightly charred. Remove and set aside.

Slice carrot into ¼ cm rounds and onion into thin discs.

Trim broccoli and asparagus to even sizes.

Cut nori into strips about 5 x 10 cm.

Sift flour into a bowl and add salt. Pour in cold sparkling water and stir lightly with a fork 6–7 times. The batter should be lumpy.

Heat 2 cm of oil in a frying pan to 180°C (365°F).

Dip vegetables in batter and fry in batches until crisp and golden.

Drain on a rack or paper towel.

Reheat broth to a simmer and add noodles to warm through.

Divide broth and noodles into bowls.