I often use Japanese Mayonnaise in my recipes and get the question: "What's Japanese Mayonnaise" ?
So here you go:

Japanese mayonnaise, typically made with rice vinegar, tastes milder, e.g. less vinegary than mayonnaise made from distilled vinegar IMHO, and is slightly yellowish in colour.
I like the Kewpie brand in plastic squeeze bottles with a Kewpie doll logo on the wrapper. Once the wrapper is removed the squishy-squeeze bottle is totally 'naked' and baby-smooth as a Kewpie doll. Do you remember them with their cute little pointed heads? They were very popular, Anne Frank mentionned in her diary that she received one on her first St Nicholas Day in the Annex from Miep and Bep.
You can find Kewpie Mayonnaise at Japanese supermarkets and even on Amazon.com :)