Wash the cucumber thoroughly and peel it into thin slices using a peeler.

Sprinkle coarse salt on the cucumber slices and gently mix to soften them.

Drain the oil from the canned tuna and shred the crab sticks into small pieces.

Chop the onion finely and soak it in cold water to reduce its sharpness.

Prepare the seasoning vinegar by mixing vinegar, sugar, and salt in a 3:1:1 ratio.

Mix the cooked rice with the prepared seasoning vinegar and let it cool slightly.

Combine the shredded crab sticks, drained tuna, and chopped onions. Add mayonnaise, pepper, and salt, then mix well.

Shape the seasoned rice into small bite-sized balls.

Wrap each rice ball with a cucumber slice, rolling it tightly.