Finely chop the kimchi and onion.
Heat sesame oil in a pan and sauté the kimchi and onion.
Drain the oil from the canned tuna and add the tuna to the pan, stir-frying together with the kimchi.
Add the sautéed kimchi and tuna, crushed sesame seeds, and sesame oil to the rice and mix well.
Shape the well-mixed rice into rice balls.
Wrap the rice balls with seaweed.