Enbu Tennis is a tennis form that is based around an ancient martial arts that Hiyoshi practices. Hiyoshi came up with this style after he entered Hyotei when Coach Sakaki noted that Hiyoshi’s following through after hitting the ball was a bit slow, and he suggested that Hiyoshi tried returning a shot in the form that was most comfortable to him. Using the martial arts he’s learned as a base for his stance in his Enbu Tennis, he’s able to play at his natural state.
Because he's playing in his natural form, he presumably doesn't have to worry about the take-back and follow-through of his shots and can remove the hesitation in his form altogether, while average players worry about their swings from the start motion until the end.
With Enbu Tennis, he’s able to return a Tannhauser Serve, a technique that almost doesn’t bounce, with his natural stance (which is quite an amazing feat, as Atobe used the Front Foot Hop, a high-level rising shot technique, to return his own Tannhauser himself).