I guess the artist found it by luck. Gem shops should have some egg-shaped gems to sell. If you can't find it, use regular eggs to make the mold (I think the soul gem is smaller though)
Definitely a quail egg, they're around 3-4cm high.
I also know some jewelry stores (and oddly enough, home furnishing outlets) sell teardrop and egg-shaped glass stones in different sizes at their DIY sections. A colored one should suffice.
Without this, nothing can start. This time, I chose to use an egg-shaped stone as gem. I like egg-shaped things, so it was between the objects I collected. I see lot of these in shops which sell "power stones" and such. Incidentally, the shop where I bought this stone comes up first if you google "原宿・天然石" [Harajuku - Tennen'ishi], it's a Cosmo store. Recommended.
N.B. This is another dangerous step to take, please prepare yourself before going. However, they're currently closed on Wednesday.Incidentally I found the stone and I thought "This is it!", and that is the only gem as it is.Let's search the raw materials.The one and only gem in the world is ready.
