I have been through all this before with something I have been toying with for years.
I have taken quotes from many sources and use them as inspiration. For example; "“You must be shapeless, formless, like water. When you pour water in a cup, it becomes the cup. When you pour water in a bottle, it becomes the bottle. When you pour water in a teapot, it becomes the teapot. Water can drip and it can crash. Become like water my friend.”" it's a Bruce Lee quote and to me that means a water style is formless and thereby can conform to whatever it is fighting against.
For fire I have it as aggressive and unrelenting. I translate that as someone using a fire style will be quick and strike often, keeping up their attacks until the enemy falls. In HARP game terms I see the Fire style as having both Acrobatics and Adrenal Speed as companion skills. A fire style user may be able to keep Adrenal Speed going much longer than a normal round as long as they keep attacking their foe(s). But for fire to burn it needs fuel, so what would fuel the extra Adrenal Speed other than having to keep attacking?
I was thinking they would not be able to use their Adrenal Defense while using their special attack skill, but if they are attacked they can reverse it and damage their foe, aka fire burns when touched.