With the Frame Arms line Kotobukiya wants to give modelers the possibility to create their own mecha model (MAMU stands for Multi Assemble Mechanical Units).
Every kit comes with the same articulated interior frame where you attach the parts you've chosen for your mecha. Parts of different Frame Arms models are interchangeable, so there's an enormous selection and lots and lots of varieties are possible.
There's a Japanese instruction with lots of comprehendible pictures included, so it's not that difficult figuring out which parts have to been put together.
