Oni Masks are often behind paywalls and not to my liking anywho, Threw this together in blender. It's a little lumpy, but it works if you tension it well.
I haven't scaled it at all - for my face, printing it out 18cm wide across worked real well. If you have a small face, maybe go for 16cm or so across. Feel free to size it to you, cut it up, support it how you see fit, etc.
Turned out really freakin cool and feels solid. Gave it a nice coat of paint and feels like the real thing.
I don't know how to cut holes in objects in blender, so the jaw and forehead are actually processes that have seperated and fused back together. I don't know how to make the back of the mask less lumpy without ruining the detail on the front so GL w that if you manage.