Very nice start to a tower defence game, I thought the music was very nice and calming. The mechanics of swiping the fire are well executed,
I would like the enemies' colliders to be a bit bigger, as the moment I have to drag along their health bars to damage them.
Also, the fire seems to be too strong, I was able to hold off the enemies very easily by swiping near their entrance and consistently upgrading my magic power. Once I started this tactic, there were never more than 1 enemy on the screen, quickly leading to a bit of boredom.
I would suggest maybe having the fire be a more basic attack that only does a little damage, and the main amounts of damage come from another source, maybe heavy spells with a cooldown or troops to be sent to meet the enemies.
The art and sound are great, it just needs some more polish and progress to really find the fun :D