I will tell you this that i'm not a lawyer.

And the legal rabbit hole is pretty scary.

Maybe if you didn't use blatant toei patent product, like sounds or logo that would fall under parody category.

Parody should fall under fair use.

So, if you have custom gaia memory with B that said banana. Maybe that can be safe... But i'm not sure.

But, on the other hand people also sell some self-made kamen rider helmet.

They didn't call it official though, that's also exist. Never call your custom product "official".

And lastly, don't go too big, don't be a competitor, don't be in their way.

That's kinda the gist of it.

They will let you off pretty easily as long you didn't get in their way of money making.