Make sushi vinegar. Add apple cider vinegar, sugar and ¼ tsp salt to a pan and dissolve over low heat.
When rice is cooked, drizzle in sushi vinegar and mix well. Leave to cool before using.
Step 2: Cook the tamago
Lightly beat the eggs with sugar. Sieve the mixture.
Lightly grease a pan with cooking oil. Pour in a portion of egg mixture. Cook over low heat till half set.
Sprinkle in some crab meat and roll up. Slide the egg roll to one side, pour in another portion of egg mixture. Repeat till egg mixture and crab meat are used up.
Step 3: Assemble the onigirazu
Place a piece of seaweed over a large plastic cling wrap. Scoop 80gm cooked sushi rice and place in the middle of the seaweed sheet. Wet your fingers and slightly spread out the rice.
Place the tamago over the rice. Spread some mayonnaise over and top with shredded cucumber.
Lastly top with 60gm of sushi rice over the cucumber. Gently press down to compact the fillings. Fold in corner with the help of the cling wrapper. Wrap the rice sandwich tightly with the cling wrap. Repeat till rice are used up.