Silicone. Bought it on Amazon

Personally I have no fear of losing it. It is secure in this holder. I do know that there are 2 "versions" of the go-tcha. One of them is a fake and a slightly different shape which I believe is likely the one that does not fit in the cases as well.

We use this one and keep it on our keychain

Cheaper and more compact

MiPhee Silicone Case for Go-tcha, Black https://www.amazon.com/dp/B07758318L/ref=cm_sw_r_cp_apa_i_8AE1BbGJVY7ZM