i wouldnt know about that personally but i am an ebay/etsy/aliexpress HOUND. i am constantly looking at things on those sites just for kicks and there are a TON of cases and pouches. specifically handmade ones on etsy, but there's a silicone one that keeps popping up repeatedly on wish and ali.
i dont THINK there's a copyright issue? theyre super popular and ive seen the same listings up for a few years now, especially the ones that are more expensive and kind of like art pieces more than they are Just a case. i doubt there would be any issues? you're selling an accessory, not ripping off the product itself, and it looks like for the crochet ones there so many patterns you can buy and its.. probably just making a decent magic circle to swallow your little egg, then including a window. i bet some of the patterns let you use THAT pattern to sell your cases, but i don't know about that.
nothing legal involving bandai at the very least, or else this would have been swat away a good while ago.