Cut carrot into small pieces and microwave with 1/2 tsp water for 1 minute.

Slice cucumber into different shapes: sticks, half-moons, and julienne. Salt the julienne cucumber and let sit for 10 minutes, then rinse and squeeze dry.

Slice tuna and salmon into thin pieces.

Mix egg with potato starch and water to create egg mixture.

Cook thin egg sheets in a lightly oiled pan, flipping before browning. Repeat until all egg mixture is used.

Slice cooked egg sheets into thin strips to make kinshi tamago.

Mix sushi vinegar ingredients (sugar, salt, vinegar) in a bowl.

Combine warm rice with sushi vinegar and mix gently. Reserve 60g rice and shape into koinobori fish using plastic wrap.

Layer sushi rice, julienne cucumber, and tuna in a container, pressing gently to flatten each layer.

Cut nori to create fish eyes and decorations.

Place layered sushi on a plate and cover with kinshi tamago.

Decorate koinobori rice shapes with carrot and cucumber scales, and attach nori eyes.