The functioning of the technique is very simple. Yūgetsu plays the flute as a distraction to the opponent's ears, which acts as a trigger to the Genjutsu. Waves of chakra are fired with each melody. They disturb the chakra of the opponent slightly, giving Yūgetsu the chance to trap them under his Genjutsu, which shouldn't be difficult considering the trigger that was initiated with the sound of the flute. The opponent is immediately trapped under the Genjutsu as soon as they hear the sound of the flute. Breaking out of the Genjutsu would not be the smartest idea since the sound created by the flute will constantly drop the opponent under Genjutsu over and over again.