In a large bowl, combine celery, rice wine vinegar, sesame oil, grated ginger, soy sauce and vegetable oil.
Add the squid slices to the marinade and stir gently for 30 minutes or longer.
Mix in red onions, green onions, sesame seeds, sugar, bamboo shoots and kikurage mushrooms. Stir to combine all of the ingredients.
Cover and refrigerate for at least one hour before serving.
Garnish with extra green onions and sesame seeds before serving.