Drain the oil from the tuna using a strainer.
Mix tuna with mayonnaise, salt, and pepper until well combined.
Prepare seaweed sheets for kimbap.
Mix rice with salt and sesame oil.
Spread the rice thinly in a triangle shape on top of the seaweed sheet.
Place the tuna mayo in the center.
Cover the tuna mayo with rice and wrap with seaweed.
Shape the onigiri using plastic wrap or a mold.