Hmm. Well, if Kick Shot's thing is kicking people with gun boots, I got a few ideas.

Level 1 Ability would be allowing Kick Shot to take firearms (as a rogue they are proficient with all firearms, including things like bows, crossbows, and specific types of throwing weapons) and allow him to use them with his kicks. As he levels up the damage he can do with the guns through his kicks are increased, and there isn't a need to reload ammo for his kicks, though he only shoots when he actually kicks something. he can still just use a gun normally if he wants.

Level 2 Ability could be your mobility/attack speed increase via gun type. Depending on which gun Kick Shot has equipped, his damage/attack speed/special traits increase or are added. If he's using shotguns the impact of his kicks are greater, if he's using some sort of automatic weapon the rate of his attacks and movement increases, if he's using something explosive his kicks have a boom to it, if it's a sniper rifle then it simply does more damage or perhaps armor piercing qualities. For pistols... Eh.

And level 3 and beyond I guess then it goes into special attacks. Maybe at three he can dual wield two types of fire arms, even if they're normally two-handed ones, but he can't use the guns normally if he does it like that. Instead each one of his legs gets the quality of one of the guns, so you can have your right leg be a machine gun for fast kicks, and the left a shotgun if you need space.

And so on and so forth. As I said, I'm playing your abilities off the angle that you'll be doing a lot of kicking.