McDonalds Japan routinely (every month or so) introduces new promotional menu items. I don’t know if any of them have become permanent additions but some of them have been quite nice. Just recently, they had a chicken-cutlet burger, with the cutlet filled with melted cheese. Tasty, but the cheese often made the cutlet split apart and slide around, so it was a bit too messy.
And the teriyaki burger is part of the standard menu.