Japanese mayonnaise (マヨネーズ)is dangerous for the unwary in Japan. It is surprisingly tasty in comparison to American mayonnaise. You may instantly become a "マヨラ(mayola)" or mayonnaise lover. Entire Japanese families are "マヨラ" and hence in danger of becoming overweight from eating too much mayonnaise.
Like the ketchup fanatic, the "マヨラ" thinks mayonnaise goes with everything, but it is normally found in a large variety of Japanese dishes. Traditionally お好み焼き（おこのみやき okonomiyaki) is topped with decorative lines of mayonnaise. Seafood pizza such as Pizza-Hut Japan offers comes with a liberal helping of mayonnaise. Many of the japanese rice balls called おにぎり(onigiri) may have mayonnaise, including the "sea chicken" type which contains tuna mixed with mayonnaise. Today I had a つくねおにぎり(tsukune onigiri, grilled ground chicken) which had a dollop of mayonnaise between the rice and the chicken. It was really tasty, but Japanese mayonnaise is a bit rich so it was a little heavy for breakfast. I love Japanese mayonnaise in very small quantities.
By the way, the kewpie doll created by Rose O'Neill is the mascot of the most popular Japanese brand of mayonnaise, which is called Kewpie Mayonnaise. Introduced in 1925, the product is overwhelmingly popular, and often called simply Kewpie.