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Using Soap Bubble Ninjutsu, the user creates acidic bubbles at their opponent that burn the opponent when popped.
Trivia[]
The san in Santōka's name is actually written with the kanji for mountain (山), but for this technique, it is interpreted as acid (酸), also pronounced san. Tōka is interpreted as meaning permeation (透過) instead of head (頭) and fire (火), which it means in Santōka's name.
Though not seen in the manga, the databook states that Utakata was capable of combining acid with his Soap Bubble Ninjutsu.