This is a custom grip for the R36S to make long play sessions more comfortable.

I made it because I saw this video by HyperPlay RPG where they showcase a custom grip: 

After asking if I could print it myself, I didn't get a reply so I did some research. It turns out their grip also remixes this model by jpjoao_nasc. They did the same small changes as I did here, but instead of giving back to the 3D print community, they decided to only sell it.

Since the original model included the Fusion360 file, it was trivial for me to make the same changes and release it for everyone, including new source files so anyone can build upon it.