Tell me the idea. I'm a computer science student with free time this summer. I can probably create it on Java if it's simple enough.

It's a Bending game, I dont know if its even possible, because I know next to nothing about scripts. You pick an element (Air, Water, Earth, and Fire,). Let's just use water. To use water, you go to a body of water, which would be on the field, and use your mouse to move and control the water. With earth you would do the same, only on the platform you stand on. Wind you just click anywhere in the sky, and fire you do the same and create fire. You go against different benders, and you can be any bender you want.

I must find it. And play it. I couldn't find any.

Keep looking. They're there, but they probably aren't as good as you'd imagine them to be.
Also, when you fought, lets say a water character against a rock character. Could the only thing u do is moving around your mouse and clicking. Or is there more to it?
And how would different elements intereact. For example, a rock will go through air... and water would evaporate in fire...