Late to the party for this topic, but I managed to stumble upon on it.
That custom made phone case is gorgeous, Rei!
My family actually owns a business that creates custom things such as clothes, pillows, phone cases, pencil cases etc. with anything you'd want on it. They used a special machine to be able to create them. They sell these items to people all over the world. I am planning to get a few things with Sigyn on them in the future.
I can tell you that if you decided to turn it into a little business, it could work out for you as many people would be interested in items with their characters on it! It's a very good business to have, and I speak from experience, as I've watched my family's business go from being a small part-time thing, to almost a fulltime thing! It's definitely worth trying out, at least, especially if you have the talent for it!
I wish you good luck in your future endeavours!