There are various theories about from where or when Kansaifu-okonomiyaki started to be made using mayonnaise and this isn't known for sure, but there is a theory that Boteju (a long-established okonomi-yaki chain famous throughout Japan) started to use it, and another theory that an individual shop started using it, and also a theory that it has been used in households for a long time.
どこでいつから関西風お好み焼きにマヨネーズをつけるようになったかは諸説あり定かではなく、ぼてぢゅうの説、個人店が最初という説、またそれ以前から家庭内で使われていたと言う説もある。