Shred the crab sticks into small pieces and finely chop the onion. Soak the onion in cold water for 5-10 minutes to remove its sharp taste, then drain well.

Mix the cooked rice with the sushi seasoning and roasted sesame seeds from the inari sushi kit. Squeeze the marinade out of the inari wrappers gently to avoid tearing them. Fill the wrappers with the rice mixture to form inari sushi.

Combine the shredded crab sticks, chopped onion, mayonnaise, and mustard in a bowl. Mix well. Add a pinch of salt and pepper if desired.