Here is how you can digitally draw fire
First of all take a simple brush scrible 2 3 colors like yellow orange in red. Like a rough fire
Then you have to earse the edges and make it look edgy and sharp just erase in zig zag
Now just blur these edges
Duplicate this fire and fill a solid yellow color on it with protect alpha on
Set this layers blending mode at screen and add a few yellow sparks n voila your fire is ready
Here is the final result
App used : Medibang
Time it took maybe 25 minutes