In the realm of anime props, this is hardly gigantic
I'd go with pink insulation foam from the hardware store. You glue together layers to get the right thickness. Make a very rough shape in two halves, and then scoop out the center such that the cavity just fits a cheap baseball bat. If it's wood (which would be best) soak the bat in water for a minute or two. Then coat the whole bat in a thin layer of Gorilla glue, set the bat in the foam, and glue the two layers together. Wrap the thing up in rope, strapping, medical bandage, or even blue painters tape as the glue cures.
Once the glue has set, carve it down to that hexagonal shape. (is that a hexagon? I can't tell, whatever it is). If you don't know how to get flat planes and proper angles, you might want to read up on woodworking a bit. the techniques are similar, but the cutting is much easier.
The circles can probably be made using something from the wood crafting section of the craft store. It'd just be a pain to have to carve them all out.
Coat the whole thing (except the handle) in paper mache Heavy paper, like the stuff for grocery bags is strongest. Once dry, mix up a slurry of paper clay mixed with a bit of water and brush it on. This helps to hide the seam lines where the pieces of paper overlap.
Once dry, sand the surface smooth (wear a dust mask) up to 220 grit. It probably actually makes more sense to glue on the circles at this point.
Prime it, paint it brown, dry-brush the circles with a light brown for highlights, wrap the handle in white athletic tape. Done!