Fellow game creators,

I have been working on my game for a while now, and I got the basic game, shop, deck, and gameplay all done, but I am now trying to come up with a theme, as the one I was going to use has been used by another game.

The Idea

The player has a grid of 3 x 5 that they can spawn starter units too; once on the field, they can use cards from their deck to evolve their unit into the better unit, think pokemon but in tower form.

E.g

Starter unit + Speed Up = Rapid attack unit.

I was planning on doing human cells and viruses as the enemy, but plague defenders came out, which is a direct copy of the art style I was planning for

https://play.google.com/store/apps/details?id=com.kraftonpnix.projectp&hl=en&gl=US

So I got to change direction, but not sure of a good theme; any ideas would be a great help