The water breathing technique in "Demon Slayer" holds great significance as it is one of the core elements of the show's plot and character development. The water breathing technique is a unique and powerful sword fighting style that allows the Demon Slayers to harness the power of water to enhance their combat abilities. It is particularly important to the main character, Tanjiro Kamado, as mastering this technique is essential for him to become a skilled Demon Slayer and fulfill his quest to avenge his family and defeat the demons. The water breathing technique also symbolizes purity, flexibility, and the ability to adapt to different situations, making it a key aspect of the overall narrative of "Demon Slayer".