So this is pretty neat. Built in 767 it is called "頭塔" (Zutou) and it is south of Todaiji and south of the Kasuga Taisha Omotesando--so south of the normal tourist area where everyone tends to visit. You have to go out of your way to find it.
While there are individuals apparently buried (or at least memorialized) at the top of the 10 meter tall stepped structure, it seems more an object of worship than anything else, and really unlike anything else I can think of. I don't know how much as been reconstructed, but some of the photos just on Google Maps show some really interesting details.
There are small roofed structures around the stone walls that cover stone Buddha images. I imagine that this has been reconstructed from what was likely a completely covered and obstructed hill, but I had no idea that it existed until this article. I'm also not aware of it being part of any particular tradition of stepped hills like this--one could point to the kofun, and maybe they were mimicking that in a Buddhist context, but I don't know if there are any other similar structures anywhere else in Japan.