The Eternal Echoing Formation (永遠に響き渡る形成; Eienni hibiki wataru keisei) is a genjutsu only seen being used by Sachiko of the Nine Guardians. When Sachiko sets up a perimeter of sealed notes with the kanji "sound" (音), she can activate this technique with a snake seal. When activated, all of the sound emitted in the affected field (with the exception of Sachiko herself. However, sound created from a noisy technique used by Sachiko still would enter and echo within the formation) will continuously bounce around the area. The sound does not fade with time, and the only method to break the genjutsu is to break the perimeter by removing the marked seals until there are only two left. Sachiko is not affected by the constantly echoing sounds, though she is incapable of hearing anything within the