Mysterious sauce

Okonomiyaki 

Okonomiyaki is like a occidental pizza. Of course, ingredients are a litte different. But shape and concept are almost same. Especially, fine slices of bonito are sprinkled. As a sauce, mayonnaise is poured along with deriyaki sauce( I think that this sauce is a typical one to Japanese, because we can smell et taste easily it on japanese food, even Macdonald's hamburger). At the first time, mayonnaise was very strange to me because we don't put this sauce onto pizza or korean pizza called as Bin dae Dduk, besides it, as I have never tasted this sauce, I couldn't imagine it. But after trying it, I couldn't yet understand how this mayonnaise went well with Okonomiyaki. How discovered it ?