Fun puzzle game with a cool mechanic. But figuring out how the game actually worked was a real hurdle for me.
Having only colors to represent game objects (except for fire) makes it very difficult at first to tell what is what. I just had to guess the difference between green, light green, and purple.
It took me a long time (until the level with the 5x5 board and corruption in the middle) to notice that the numbers in the top left had to do with why my movement mechanics kept changing from level to level. Some tips to help that out without adding a tutorial would be to make the text pulse whenever you make a move/light a fire and make it turn red when it's exhausted for the turn. And having a move sound effect that drops in pitch with each subsequent move (and an error sound when you fail to move) would help even further.
It completely eluded me that "rounds until rain" was just another way of saying, "turns remaining". I thought it was a game mechanic where all my fires would be put out every n turns, so I could light fires right before a rain without worrying about them spreading. Having text on the "you lose" screen that explains why you lost could help with that.
I wish there were some tougher puzzles later in the game that required more turns and fighting out more than two sources of corruption at once. The game felt pretty easy.
But overall, I think this mechanic was used well in the puzzles it was in. Nice work!