Obito Uchiha's ocular prowess was extraordinary. Not only could he easily control a shinobi of the Fourth Mizukage's caliber with genjutsu, but in the original storyline, he had even been able to control the Fourth Mizukage after he had become a perfect Jinchuriki... In theory, when a perfect Jinchuriki was caught in genjutsu, the Tailed Beast within him would help dispel it. However, Obito had probably cast the genjutsu on both the Jinchuriki and the Tailed Beast at the same time.
Yet no matter how powerful Obito's ocular prowess was, he had only used ordinary genjutsu, not genjutsu exclusive to the Sharingan. Therefore, once someone realized that the Fourth Mizukage was under genjutsu, it was possible to break Obito's genjutsu through conventional means.
What Yuhara had done was essentially swing his arms wide and slap the dazed Fourth Mizukage several times across the face. Afterward, he looked at the Mizukage's reaction and thought, Er... it seems to have worked pretty well.
Seeing the Fourth Mizukage's expression change from vacant confusion to slightly bewildered pain, Yuhara knew he had done another good deed. He just had no idea whether the other party would appreciate it.
Yuhara released the Fourth Mizukage and quickly retreated several steps before saying, "Mizukage-sama, I'm very sorry. Because of the impact of my Chakra, you've temporarily lost the ability to move. The good news is that we've helped you break free of the genjutsu... Do you remember when and how you fell under it?"
The Fourth Mizukage knelt half-kneeling on the surface of the water. He looked at Yuhara and then said, "The Konoha Ninja I met at the Five Kage Summit... Why are you in the Land of Water?"
Yuhara glanced at Kakashi and Tenzo on the other side and signaled them with his eyes. "There's