This little object, made by Tenga (and not sold by Muji) is almost certainly not what you think it is. Of course, if you were thinking “self-contained disposable vagina-like environment,” then I beg your pardon. Because that’s exactly what it is.
The Egg appears to be a silicone shell with one of a variety of textures on the inside — I’ll let the manufacturer do the describing:
Three different types of structure.
・ EGG WAVY … PURUPURU stimulation of continuous wave!
・ EGG CLICKER … stimulation of the process often large and small!
・ EGG SPIDER … KUKKIRI produce eye irritation ami!
I can’t think of a better way to put it. If you’re curious how it works, check out the SFW how-to video (very methodical).