1. In a small bowl, add fish, cooking sake and katakuriko/potato starch. Mix and let it sit for about 10min.
2. In a medium bowl, add the fish from #1 and ingredients A. Mix well until combined.
3. Lay a spring roll wrap flat, tip down. Place the filling mixture centered on the wrap. Roll up tightly. Dab a little 'glue' mixture along the edges to seal (right, left, then roll as per picture). Repeat until you use up the filling mixture.
4. Pour enough oil in a wok or large saucepan and heat on medium-high until hot : Stick in a bamboo chopstick, if bubbles appear, it's hot enough. Place the rolls gently in the oil and cook from both sides, turning occasionally, until nicely and evenly golden. Transfer them to a plate lined with paper towels to drain the excess oil. Repeat with the remaining spring rolls.
5. Make the sauce In a small bowl, add all the sauce ingredients and mix.