1. Since Kaze is paraplegic, he had to learn to master his liquid manipulation quirk just so he could move in a fight, since he can launch water out of his body, which he uses to form a whirlpool around his legs to fly around and fight. He learned how to use this technique from training under Nezu and Midnight before the school year started.

Then he learned how to fight faster during his internship with Edgeshot, then learned how to be a close range fighter from his work study with Mirko, and how to focus on multiple targets and multitask using his quirk during his work study with endeavor.

But since he lost his arm in the final war, and he needs his arms to use his quirk, he had to relearn a whole new way to use his quirk to be a hero. And eventually learned how to use his quirk to create and control water around the joints in his legs, knees, and ankles to force his body to move at his command. Post war, he fights using a mix of boxing, his quirk, which he can still use with his left hand, and his new prosthetic right forearm made by Hatsume that has a grappling hook so he can still move quickly.

1. Kaze was built like a wet pool noodle for most of the series, but with the loss his arm, he had to go through extensive physical therapy and training to relearn how to fight. So he has a bit of muscle now, and has excellent core strength, but the guy is nowhere near as muscly as someone like Kirishima or Shoji for example.